University  of  California  •  Berkeley 


Technical  Paper  90 

DEPARTMENT  OF  THE  INTERIOR 
BUREAU     OF     MINES 


JOSEPH  A.  HOLMES,  DIRECTOR 


METALLURGICAL  TREATMENT  &*&• 
OF  THE  LOW-GRADE  AND  COMPLEX  ORES 

OF  UTAH 

A  PRELIMINARY  REPORT 


BY 


D.  A.  LYON,  R.  H.  BRADFORD,  S.  S.  ARENTZ, 
O.  C.  RALSTON,  and  C.  L.  LARSON 


ISSUED  JOINTLY  BY  THE  BUREAU  OF  MINES  AND  THE  DEPARTMENT  OF  METAL- 
LURGICAL RESEARCH  OF  THE  ENGINEERING  STATION 
OF  THE  UNIVERSITY  OF  UTAH 


WASHINGTON 
GOVERNMENT  PRINTING  OFFICE 

1915 


The  Bureau  of  Mines,  in  carrying  out  one  of  the  provisions  of  its  organic 
act — to  disseminate  information  concerning  investigations  made — prints  a  lim- 
ited free  edition  of  each  of  its  publications. 

When  this  edition  is  exhausted,  copies  may  be  obtained  at  cost  price  only 
through  the  Superintendent  of  Documents,  Government  Printing  Office,  Wash- 
ington, D.  C. 

The  Superintendent  of  Documents  is  not  an  official  of  the  Bureau  of  Mines. 
His  is  an  entirely  separate  office,  and  he  should  be  addressed : 

SUPERINTENDENT  OF  DOCUMENTS, 

Government  Printing  Office, 

Washington,  D.  C. 

The  general  law  under  which  publications  are  distributed  prohibits  the  giving 
of  more  than  one  copy  of  a  publication  to  one  person.  The  cost  of  this  publica- 
tion is  5  cents. 

First  edition.    March,  1915. 


CROI  1    I  IBKARY 


CONTENTS. 


Page. 

Introduction,  by  D.  A.  LYON 5 

The  problem  of  Utah's  low-grade  ore,  by  ROBERT  II.  BRADFORD 7 

Review  of  mining  in  Utah 7 

Gold 7 

Silver 7 

Lead 8 

Copper 8 

Zinc 8 

•             Improvements  in  mining  and  methods  of  treatment 8 

Porphyry  mining  at  Binghain 9 

Treating  stope  fillings  at  Park  City 10 

Low-grade  ore  in  the  Tintic  district 10 

Situation  and  extent  of  the  low-grade  ores,  by  S.  S.  ARENTZ 10 

Examination  of  the  mining  districts • 11 

Bingliam  and  Garfield 11 

Park  City  district 11 

The  milling  problem  in  the  Park  City  district 13 

The  metallurgical  problem  in  the  Park  City  district 14 

Tintic  district 14 

Stockton  district 1C 

Dry  Canyon  and  Ophir  district , 17 

Deep  Creek  district 17 

Milford  district 17 

Silver  Reef  district _• 19 

Eastern  Utah 20 

Chemical  characteristics  of  the  Utah  ores,  by  O.  C.  RALSTON 21 

Results  of  analyses 21 

Types  of  ores  analyzed 22 

Metallurgical  treatment  of  the  ores,  by  D.  A.  LYON,   R.   H.   BRADFORD, 

S.  S.  ARENTZ,  O.  C.  RALSTON,  and  C.  L.  LARSON 24 

Processes  of  treatment 24 

Oxidized  ores i 24 

Complex  sulphide  ores 25 

Removal  of  copper 26 

Chief  metallurgical  problems 26 

Treatment  of  oxide  and  carbonate  ores 26 

Treatment  of  zinc-bearing  ores 26 

Chloridizing  processes 28 

Holt-Dem  process .     28 

Principal  features  of  process 29 

Factors  affecting  the  process '. 29 

Summary 30 

Knight-Christensen  process 31 

3 


CONTENTS. 

Metallurgical  treatment  of  the  ores — Continued.  page. 

Processes  having  a  possible  application  to  Utah  ores 32 

Lead  carbonates  carrying  silver 32 

Murex  process 32 

Sulphidizing  and  flotation 32 

Electrostatic  separation 32 

Oxidized  copper  ores  carrying  gold  and  silver 33 

Chloridizing  and  leaching 33 

Sulphidizing  and  flotation 33 

Mosher-Ludlow  process 33 

Slater  process 33 

Other  processes 33 

Oxidized  zinc  ores,  occasionally  carrying  gold  and  silver 34 

Igneous  concentration 34 

Leaching  with  ammonium  carbonate  solution 34 

Bisulphite  process 34 

Leaching  with  acid  solution  and  electrolytic  precipitation  of 

zinc 34 

Oxidized  zinc-lead  ores,  carrying  occasionally  gold  and  silver 36 

Bisulphite  process 35 

Leaching  with  ammonium  carbonate  solution 35 

Sulphidizing  and  flotation 35 

Oxidized  ores  of  zinc  and  copper,  carrying  gold  and  silver 35 

Leaching  with  ammonium  carbonate  solution 35 

Bisulphite  process 36 

Leaching  with  acid  solution  and  electrolytic  precipitation 36 

Igneous  concentration 36 

Oxidized  ores  carrying  zinc,  copper,  lead,  silver,  and  gold 36 

Partly  oxidized  sulphide  ores. 36 

Raw  materials  for  use  as  reagents 36 

Iron  for  precipitation 37 

Sodium  sulphate  (mirabilite) 38 

Allied  problems 38 

Conclusion 39 

Publications  on  treatment  of  minerals—  40 


METALLURGICAL  TREATMENT  OF  THE   LOW-GRADE 
AND  COMPLEX  ORES  OF  UTAH. 


INTRODUCTION. 

By  D.  A.  LYON. 

In  the  performance  of  its  duty  of  conducting  investigations  to 
increase  safety,  efficiency,  and  economic  development  in  the  mining 
and  treatment  of  ores  and  minerals  the  Bureau  of  Mines  is  cooperat- 
ing with  various  State  organizations  in  order  that  the  necessary 
work  may  be  done  to  best  advantage  and  without  duplication  of 
effort. 

At  its  tenth  regular  session  in  1913  the  Legislature  of  the  State  of 
Utah  provided  for  the  establishment  of  a  metallurgical  research 
department  in  connection  with  the  State  School  of  Mines  of  the 
University  of  Utah.  The  act  °  providing  for  this  department  stated : 

The  purposes  of  this  research  department  shall  be  to  conduct  experiments 
and  researches,  either  alone  or  in  cooperation  with  the  National  Bureau  of 
Mines  and  other  agencies,  with  a  view  of  finding  ways  and  methods  of  profit- 
ably treating  low-grade  ores,  of  obtaining  other  information  that  shall  have  for 
its  object  the  benefit  of  the  mining  industry  and  the  utilization  and  conserva- 
tion of  the  mineral  resources  of  the  State,  and  to  publish  and  distribute  bulle- 
tins and  articles  relating  to  the  department  and  its  work. 

The  station  has  effected  a  working  arrangement  with  the  Federal 
Bureau  of  Mines  by  which  the  bureau  is  furnishing  the  metallurgist, 
who  has  charge  of  the  research  department,  and  an  assistant  metal- 
lurgist. The  University  of  Utah  is  providing  the  buildings  and 
equipment  and  also  five  metallurgical  research  fellowships  of  the 
yearly  value  of  $720  each.  The  fellowships  are  awarded  to  gradu- 
ates of  colleges,  and  preferably  mining  schools,  who  have  shown 
special  aptitude  for  research  investigations.  Holders  of  the  fellow- 
ships are  required  to  work  on  the  bureau  time  schedule,  except  Sat- 
urday, when  they  quit  at  noon.  Their  employment  extends  over  the 
entire  12  months. 

The  fellows  selected  by  the  university  authorities  for  the  fiscal 
year  1913-14  were:  L.  F.  Pattison,  A.  B.,  University  of  Utah;  W.  G. 

«  Laws  of  Utah,  1913,  ch.  102,  sec.  2,  pp.  199-200. 


6  TREATMENT   OF   LOW-GRADE   ORES. 

Woolf ,  A.  B.,  University  of  Utah ;  O.  H.  Pierce,  A.  B.,  University  of 
Nebraska ;  A.  E.  Gartside,  A.  B.,  University  of  Oklahoma ;  and  C.  Y. 
Pfoutz,  E.  M.,  University  of  California. 

Messrs.  Pattison,  Gartside,  and  Pfoutz  resigned  their  fellowships 
at  the  end  of  the  fiscal  year,  and  those  selected,  from  a  large  number 
of  applicants,  to  take  their  places  for  the  fiscal  year  1914rl5  were: 
R.  M.  Isham,  Ph.  D.,  Columbia  University;  C.  L.  Larson,  E.  M., 
University  of  Minnesota;  and  H.  J.  Morgan,  A.  B.,  Stanford  Uni- 
versity. 

All  of  the  men  mentioned  actively  aided  in  obtaining  the  data  used 
in  preparing  this  report. 

Attention  is  called  to  the  fact  that  this  report  is  a  preliminary 
statement  only.  Much  work  must  be  done  to  determine  the  applica- 
bility or  the  precise  value  of  most  of  the  different  methods  of  ore 
treatment  that  are  mentioned. 


THE  PROBLEM  OF  UTAH'S  LOW-GRADE  ORE. 

By  ROBERT  IT.  BRADFORD. 
REVIEW   OF   MINING   IN   UTAH. 

When  the  ores  from  the  head  of  Little  Cottonwood  Canyon  were 
shipped  by  wagon  to  San  Francisco  and  by  boat  from  there  to 
Swansea,  Wales,  their  value  per  ton  was  necessarily  high.  These 
were  surface  ores,  and  the  value  decreased  with  depth.  However, 
at  the  Emma  and  neighboring  mines  at  Alta,  the  ores  continued  of 
sufficient  value  to  warrant  shipping  by  team  to  Omaha  and  thence 
by  train  to  the  smelters  at  Chicago.  Early  mines  in  other  districts 
added  to  the  amounts  shipped  to  the  distant  smelters,  but  none  of 
the  mines  of  these  districts  yielded  ores  of  enormous  value,  as  have 
many  of  the  mines  of  the  neighboring  States.  Utah's  high  standing 
as  a  mining  State  has  resulted  from  her  enormous  supply  of  medium 
and  low  grade  ores. 

GOLD. 

Utah  has  produced  some  free-gold  ores,  but  these  were  seldom  very 
rich  and  were  never  found  in  any  considerable  quantity.  The 
gravels  of  Bingham  Canyon  yielded  placer  gold  for  a  time,  as  did 
also  gravels  near  some  other  early  mining  camps.  Mines  near  Rich- 
field, in  Sevier  County,  produced  some  "  picture  rock  "  and  ore  con- 
taining enough  finely  disseminated  free  gold  to  pay  handsomely 
when  cyanided.  A  few  other  districts  have  produced  some  gold, 
but  Mercur  has  given  by  far  the  greatest  returns  as  a  strictly  gold 
camp.  The  gold  ore  of  Mercur  was  low  grade  and  could  not  have 
been  treated  profitably  but  for  the  advent  of  the  cyanide  process, 
just  when  all  old  processes  had  failed.  So  even  in  the  case  of  gold 
ores  the  State  of  Utah  has  produced  the  lower  grades. 

SILVER. 

Silver  ore  richer  than  that  now  mined  was  common  at  most  of  the 
early  camps.  Later  developments  showed  increased  tonnage,  but  of 
lower  grade.  From  the  first  mining  efforts  in  Utah  the  State  has 
ranked  high  in  silver  production.  To-day  much  low-grade  silver 
ore  awaits  some  cheap  method  of  treatment. 


8  TREATMENT   OF    LOW-GRADE    ORES, 

LEAD. 

Lead  ore  mined  for  lead  alone  must  carry  a  high  percentage  of  the 
metal  to  have  much  value  per  ton.  In  Utah  the  lead  ores  mined  have 
been  rich  in  silver,  and  it  was  the  combined  lead  and  silver  content 
that  made  the  ores  valuable.  Much  low-grade  lead  ore  and  lead- 
zinc-silver-gold  ore  is  awaiting  some  cheaper  method  of  treatment. 

COPPER. 

For  the  first  20  years  of  the  State's  mining  history  the  red  metal, 
copper,  was  not  considered  valuable.  In  the  last  20  years  the  copper 
production  has  increased  until  now  Utah  ranks  a  close  fourth 
among  the  States  of  the  Union  in  the  production  of  that  metal. 
Low-grade  copper  ores  are  the  source  of  the  copper. 

ZINC. 

Up  to  date  no  zinc  smelter  has  been  built  in  Utah,  but  not  because 
the  ores  mined  contained  no  zinc.  To  keep  down  the  zinc  content, 
because  of  the  penalty  charged  by  the  smelters,  has  been  the  im- 
portant aim  of  the  ore  shipper.  Now  the  proportion  of  zinc  is  in- 
creasing and  the  zinc  must  be  considered  as  a  possible  source  of 
profit  in  mixed  sulphide  ores  and  also  in  oxidized  ores.  Occasion- 
ally the  percentage  of  zinc  is  sufficient  to  make  the  ore  worth  ship- 
ping direct  to  zinc  smelters,  but  the  amount  of  such  ore  found  has 
been  small.  Zinc  ores,  so  long  considered  as  of  no  value,  now  bid 
fair  to  become  a  big  source  of  income  if  methods  of  profitably  treat- 
ing the  low-grade  ores  can  be  discovered. 

IMPROVEMENTS  IN  MINING  AND  METHODS  OF  TREATMENT. 

The  first  smelting  furnace  was  erected  at  Bingham  with  the 
hope  that  the  cost  of  mining  and  smelting  would  be  less  than  $100 
per  ton,  which  had  been  the  cost  of  mining,  shipment  to  Chicago, 
and  smelting  there.  Actually,  the  cost  with  this  furnace  was  kept 
down  to  $89  per  ton,  and  as  improvements  in  design  and  operation 
were  made  the  cost  was  still  further  reduced. 

As  the  mining  and  treatment  costs  were  lowered,  ores  of  less  value 
were  mined  at  a  profit.  During  the  seventies  ores  valued  below  $40 
to  $50  per  ton  were  considered  too  low  grade  to  save.  In  the  early 
nineties  methods  had  been  so  improved  that  $20  ore  was  successfully 
handled,  and  under  favorable  conditions  $16  ore.  Ten  years  later 
$8  to  $9  ore  was  worked  and  under  certain  conditions  a  profit  was 
made  on  $6  ore. 

With  the  enormous  deposits  of  low-grade  ores  the  principal  prob- 
lem demanding  attention  is  still,  as  before,  the  devising  of  cheaper 
methods  of  mining  and  treatment. 


THE   PROBLEM    OF   UTAH'S   LOW-GRADE    ORE.  9 

PORPHYRY  MINING   AT  BINGHAM. 

It  is  interesting  to  note  the  results  of  the  improvements  already 
made.  Compare,  for  instance,  the  costs  for  mining  and  smelting 
high-grade  ore  at  Bingham  in  1872  ° — $89  per  ton — with  the  costs  for 
ores  at  the  same  camp  41  years  later,  when  the  porphyry  copper  ores 
were  mined,  milled,  and  smelted  for  $1.25  per  ton. 

In  order  to  bring  the  costs  down  to  this  figure  the  Utah  Copper 
Co.  is  conducting  work  on  a  mammoth  scale.  The  company  is  min- 
ing an  entire  mountain,  the  largest  developed  ore  body  in  the  world, 
and  has  an  enormous  equipment.  Fifty-one  locomotives  and  22 
steam  shovels  are  day  and  night  engaged  in  tearing  down  the  ore. 
Every  24  hours  about  24,000  tons  of  ore  and  nearly  double  this 
amount  of  overburden  are  moved,  the  pay  ore  to  mill  bins,  the  waste 
to  near-by  gulches. 

The  feat  of  solving  the  problem  of  treating  these  ores  was  accom- 
plished by  careful  and  painstaking  experimental  research  on  the  part 
of  the  management  of  the  company.  Success  was  largely  due  to 
its  ability  to  anticipate  the  results  of  mining  and  milling  on  a  scale 
commensurate  Avith  the  immensity  of  the  low-grade  ore  body  in  the 
monzonite-porphyry  it  had  carefully  prospected.  The  company  has 
expended  $25,000,000  in  improving  its  property,  and  produces  yearly 
8,000,000  tons  of  ore,  from  which  it  extracts  over  150,000,000  pounds 
of  copper.  These  results  illustrate  the  application  on  an  enormous 
scale  of  methods  devised  for  one  class  of  Utah's  low-grade  ores. 

However,  the  Utah  Copper  Co.  still  has  its  problems.  Enormous 
quantities  of  monzonite  are  mined  and  treated  at  remarkably  small 
cost  per  ton,  but  the  fact  remains  that  the  saving  is  low.  For  each 
2  pounds  of  copper  recovered  by  milling,  a  third  pound  goes  to  the 
dump.  To  better  this  saving  while  keeping  the  cost  of  treatment  at 
a  minimum  is  the  company's  constant  effort. 

Considerable  of  the  ore  shows  a  mixture  of  sulphides  and  oxides 
of  copper.  To  keep  the  oxides  from  going  to  the  tailings  and  being 
wasted  requires  a  different  treatment  from  that  now  employed 
in  the  two  mammoth  mills.  A  method  of  leaching  combined  with 
flotation  is  being  worked  out  for  this  ore. 

The  oxidized  capping  as  a  rule  carries  considerable  copper,  in 
many  places  as  much  as  the  porphyry  ore,  and  the  copper-bearing 
capping  is  kept  separate  from  the  more  barren  waste  rock  that  has 
to  be  removed.  The  treatment  of  the  enormous  amount  of  low- 
grade  ore  in  this  capping  is  a  gigantic  problem.  More  than  40,000,- 
000  tons  of  such  ore  is  awaiting  treatment  by  a  process  that  will 
successfully  and  economically  recover  the  contained  metal.  If  such 

0  Boutwell,  J.  M.,  Economic  geology  of  the  Bingham  mining  district,  Utah  :  Prof.  Paper 
38,  U.  S.  Geol.  Survey,  1905,  p.  90. 
79474° — 15 2 


10  TREATMENT   OF    LOW-GRADE    ORES. 

ores  be  leached,  as  they  probably  will  be,  it  will  be  necessary  to 
employ  a  process  that  can  be  applied  on  a  scale  commensurate  with 
the  size  of  the  deposit. 

TREATING   STOPE  FILLINGS  AT  PARK  CITY. 

In  the  Ontario  mine  at  Park  City,  Utah,  the  material  of  too  low 
a  grade  to  be  treated  at  a  profit  was  either  not  mined  or  was  stored 
in  stopes,  or  rooms,  underground.  To-day,  because  of  improved 
methods  of  treatment,  these  old  stope  fillings  and  the  low-grade  ores 
in  place  are  being  profitably  mined  and  milled.  The  management 
states  that  the  new  mill  of  the  Mines  Operating  Co.  treats  150  tons 
of  ore  a  day.  Similar  ores  in  the  near-by  mines  are  amenable  to 
the  same  process  of  treatment  and  will  no  doubt  be  economically 
worked  in  mills  now  being  designed. 

LOW-GRADE   ORE    IN    THE    TINTIC    DISTRICT. 

In  the  Tintic  district  the  better-grade  ores  have  been  shipped  to 
the  smelters  in  the  Salt  Lake  Valley,  or  else  have  been  milled.  Some 
of  the  early  methods  of  milling  were  quite  crude.  Ores  high  in 
silica,  and  hence  hard  to  smelt,  that  carried  a  metal  content  valued 
at  less  than  $10  per  ton,  were  either  left  in  the  mine  or  stored  on  the 
dumps.  These  low-grade  deposits  are  known  to  be  large.  Of  late 
much  research  has  been  conducted  with  a  view  to  devising  some 
method  of  treating  these  ores.  A  mill  is  now  being  tested  in  Silver 
City  which  bears  promise  of  giving  desired  results. 

The  three  districts  mentioned  are  the  largest  in  Utah,  and  their 
untreated  ores  have  been  measured  in  tons.  Ores  in  smaller  camps 
promise  much  profit  when  cheap  methods  of  handling  and  treating 
are  worked  out.  The  "  porphyry  ores  "  of  the  mammoth  deposits  at 
Bingham  remained  uninviting  for  years. 

Ore,  after  all,  is  a  relative  term,  one  definition  being  as  follows: 
"A  metalliferous  mineral  containing  metals  in  sufficient  proportions 
to  be  profitably  extracted."  Hence  minerals  that  once  were  dis- 
carded as  waste  may  later  be  classed  as  ore,  and  material  that  is  con- 
sidered valueless  in  one  region  may  be  deemed  ore  in  a  region  more 
favorably  situated.  The  deciding  factor  in  the  classification  is  the 
cost  of  treating  the  material  to  obtain  its  marketable  product. 

SITUATION  AND  EXTENT  OP  THE  LOW-GRADE  ORES. 

By  S.  S.  ARENTZ. 

In  considering  what  investigations  would  be  most  profitable  to 
take  up  in  connection  with  the  low-grade  ore  problem  it  at  once 
became  evident  that  each  low-grade  ore  presents  its  own  problem  and 
that  a  survey  of  the  State  to  determine  the  location  and  extent  of  the 
developed  low-grade  ore  deposits  was  necessary.  Considerable  time 


SITUATION    AND  EXTENT   OF    THE   LOW-GRADE   ORES.  11 

and  attention  have  been  given  to  the  examination  of  reported  large 
low-grade  ore  deposits  and  tailings  dumps.  Some  of  them  have 
proved  to  be  most  inviting,  whereas  others  have  not.  A  report  of  the 
results  of  the  examinations  made  of  the  mining  districts  visited  is 
given  here. 

EXAMINATION  OF  THE   MINING  DISTRICTS. 
BINGHAM    AND    GARFIELD. 

The  mammoth  deposits  of  moiizonite  porphyry0  at  Bingham, 
previously  mentioned,  carry  small  percentages  of  copper,  silver,  and 
gold.  The  ore  is  low  grade,  but  is  mined  in  great  quantity  and  is 
treated  by  concentration  and  smelting.  The  tailings,  which  carry 
0.6  per  cent  copper,  make  an  enormous  pile.  Over  30,000,000  tons  of 
this  material  now  collected  may  yet  be  re-treated. 

The  ore  under  the  capping  and  above  the  sulphides,  consisting  of 
oxides  and  sulphides  intermixed,  will  need  special  treatment.  A 
combination  of  flotation  and  leaching  is  suggested. 

The  oxidized  ore  of  the  capping  has  been  carefully  saved  and  will 
doubtless  be  leached. 

The  treatment  of  pyritiferous  ores  with  a  low  copper  content  has 
long  been  a  problem  of  the  mines  in  this  district.  When  the  zinc 
content  is  below  8  per  cent  this  material  smelts  well  in  blast  furnaces 
running  "  pyritically." 

Ores  high  in  silica  and  low  in  copper  are  sold  to  the  smelters  for 
flux  in  the  basic-lined  copper  converters.  If  these  ores  could  be 
leached  to  a  better  advantage,  the  district  no  doubt  could  supply  a 
large  tonnage  of  such  ore.  Complex  sulphide  ores  are  also  produced 
in  this  district.  Their  treatment  has  long  been  a  much-discussed 
problem.  At  the  Midvale  mill  of  the  United  States  Co.  the  ore  is 
concentrated,  then  the  middlings  are  dried  and  treated  electrostat- 
ically. The  company  ships  a  zinc  concentrate  east  to  the  "  gas  belt>" 
but  smelts  the  lead  concentrates  and  also  the  pyrite.  Much  ore  of 
this  class  is  demanding  attention. 

PARK    CITY    DISTRICT. 

Mining  has  been  conducted  at  Park  City1  since  1869,  and  many 
dividend-paying  mines  have  been  developed,  so  that  operators  in  that 
district  are  rather  averse  to  admitting  that  anything  like  a  low-grade 
or  complex  ore  problem  exists  there. 

a  For  a  discussion  of  the  geology  of  the  ore  deposits,  see  Boutwell,  J.  M.,  Economic 
geology  of  the  Bingham  mining  district :  Prof.  Paper  38,  U.  S.  Geol.  Survey,  1905,  413  pp. 

6  For  a  description  of  the  geology  of  the  ore  deposits,  see  Boutwell,  J.  M.,  Geology  and 
ore  deposits  of  the  Park  City  district :  Prof.  Paper  77,  U.  S.  Geol.  Survey,  1912,  231  pp. 


12  .      TREATMENT   OF   LOW-GRADE   ORES. 

In  this  district  there  are  three  classes  of  ore,  as  follows : 

1.  Shipping  ore. 

Sulphide : 

(a)  Silver-lead  ore. 

(b)  Silver-lead-zinc  ore. 
(<?)    (Rarely)  zinc  ore. 

Oxidized : 

(a)  Silver-lead  ore. 

(b)  (Rarely)    zinc  ore. 

2.  Concentrating,  or  mill  ore. 

Sulphide : 

(a)  Silver-lead  ore. 

(b)  Silver-lead-zinc  ore. 

(c)  Zinc-iron-lead  ore. 
Oxidized : 

(Rarely)  silver-lead  ore. 

3.  Low-grade  oxidized  ore. 

(a)  Oxidized  silver-lead  ores. 

(b)  Oxidized  silver-lead-zinc  ores. 

(c)  (Rarely)  oxidized  zinc  ore. 

There  is  a  large  amount  of  each  of  the  above  classes  of  ore  in  the 
Park  City  and  Alta  districts.  Owing  to  the  nature  of  the  deposits 
the  total  available  tonnage  could  not  be  determined  even  approxi- 
mately. The  production  of  Park  City  for  1913  was  approximately 
as  follows:  Shipping  ore,  35,000  tons;  concentrating  ore  sent  to 
mills,  188,814  tons;  concentrates,  41,970  tons.  This  production  will 
be  maintained  for  years,  according  to  men  who  are  familiar  with 
the  district.  To  lessen  the  economic  waste  resulting  from  present 
methods  of  treating  these  ores  and  mineral  products  will,  in  the 
aggregate,  add  millions  to  the  wealth  of  Utah. 

The  five  ores  given  under  "  Shipping  ore  "  in  the  classification  are 
resolvable  into  two  classes  as  far  as  the  smelters  are  concerned, 
namely,  lead  ore  and  zinc  ore.  The  zinc  remaining  in  lead  ore 
brings  no  return  to  the  shipper,  and  if  it  exceeds  a  certain  percent- 
age causes  the  ore  to  be  penalized  so  that  the  shipper  suffers  a  direct 
loss  as  well.  Lead  remaining  in  zinc  ore  represents  a  loss — in  most 
cases  a  direct  loss.  The  loss  that  occurs  when  treating  ores  such  as 
those  above  mentioned  is  illustrated  by  a  published  statement  of  a 
Montana  producer  of  zinc  concentrate." 

The  recovery  was  high— 90  per  cent— and  the  grade  of  the  concentrate  was 
good — 50  per  cent  zinc — but  it  contained  also  small  percentages  of  lead  and 
copper,  with  some  silver  and  gold.  The  gross  value  of  the  merchantable  metals, 

0  Editorial ;  The  western  metallurgical  field ;  the  complex-ore  problems :  Met.  and  Chem. 
Eng.,  vol.  12,  September,  1914,  p.  555. 


SITUATION   AND  EXTENT  OF   THE   LOW-GKADE   ORES.  13 

based  on  current  quotations,  was  about  $80  per  ton  of  concentrate.  The  actual 
market  value  at  the  smelter  was  about  $24,  leaving  a  difference  of  $56.  A  part 
of  this  difference  is  accounted  for  in  freight,  smelting,  and  marketing  charges, 
but  much  of  it  probably  represents  a  loss  to  the  producer  due  to  economic  con- 
ditions in  the  smelting  industry.  Such  instances  emphasize  the  limitations 
of  present  methods  of  concentration  and  increase  the  demand  for  new  processes 
that  are  more  efficient. 

It  is  quite  probable  that  the  Park  City  district  still  has  a  long 
life  before  it,  during  which  time  ore  will  be  shipped  direct  to  smelt- 
ers. The  loss  of  lead  in  zinc  ore  and  of  zinc  in  lead  ore  during  this 
period  will  amount  to  millions  of  dollars  unless  some  process  is  de- 
vised for  the  saving  of  these  metals. 

In  the  milling  of  the  Park  City  ores  it  is  doubtful  if  any  consid- 
erable part  of  the  metals  in  oxidized  ores  sent  to  the  concentrator  is 
saved.  This  is  acknowledged  by  the  operators,  yet  such  ore  con- 
tinues to  be  sent  to  the  mill.  If  this  oxidized  ore  is  low  in  silver  and 
gold  content,  and  too  low  in  lead  and  zinc  to  warrant  shipping,  it 
could  not  be  treated  by  any  known  (commercially  economical)  proc- 
ess whereby  a  saving  in  lead  and  zinc  could  be  made  without  a  pro- 
portional economic  loss — that  is,  a  loss  in  smelting  as  well  as  in 
the  tailings. 

THE    MILLING    PROBLEM    IN    THE    PARK    CITY    DISTRICT. 

The  problem  constantly  before  the  mill  operators  of  Park  City  is 
to  keep  low  the  zinc  content  of  the  lead  concentrates  and  the  iron 
and  lead  content  of  the  zinc  concentrates.  All  the  zinc  in  the  lead 
concentrate  is  a  loss  to  the  operator  and  an  economic  loss  to  the 
Nation.  The  same  is  true  of  lead,  copper,  and  other  metals  in  the 
zinc  concentrate. 

That  a  problem  does  exist  in  the  treatment  of  the  milling  ores  of 
Park  City  is  proven  by  the  fact  that  for  years  the  tailings  carried 
down  Empire  Canyon  and  Woodside  Gulch  have  been  re-treated  in 
a  crude  way  by  privately  owned  plants  equipped  with  concentrating 
machinery  similar  to  that  in  the  company  mills. 

The  tailings  carried  down  these  waterways  are  retarded  at  in- 
tervals by  rough  dams.  From  time  to  time  the  material  caught  above 
a  dam  is  shoveled  into  piles,  gathered  into  wagons,  and  hauled  to 
a  crude  mill  farther  down  the  gulch,  where  the  valuable  minerals 
are  extracted  by  means  of  jigs  and  tables.  Enough  of  these  min- 
erals is  extracted  to  leave  a  fair  profit  after  it  has  been  shoveled  at 
least  three  times,  hauled  1  to  3  miles,  and  treated. 

A  somewhat  similar  condition  exists,  perhaps,  at  any  of  the  silver- 
lead-zinc  concentrating  plants  throughout  the  Western  States.  That 
it  does  exist  merely  goes  to  prove  that  some  losses  occur  even  at  such 
successful  plants  as  those  of  Park  City. 

Other  than  the  above-mentioned  ores,  there  is  a  variety  of  oxidized 
ore  containing  6  to  8  ounces,  or  more,  of  silver  per  ton  and  0.5  to  1  per 


14  TREATMENT   OF   LOW-GRADE   ORES. 

cent  copper.  This  ore  may  be  the  filling  of  fissures,  replacement 
material  at  intersection  of  fissures,  or  a  bedded  deposit,  and  may  be 
material  derived  from  high-grade  ore  or  may  be  a  distinct  body  of 
low-grade  ore. 

THE  METALLURGICAL  PROBLEM  IN  THE  PARK  CITY  DISTRICT. 

Although  it  would  not  be  commercially  feasible  to  attempt  a  per- 
fect extraction  of  all  the  valuable  minerals  from  an  ore,  it  would 
seem  that  a  better  extraction  should  be  had  than  50  to  66  per  cent  of 
the  zinc  content,  as  is  stated  to  be  obtained  at  the  Park  City  mills. 
It  is  not  meant  by  this  statement  that  the  mills  are  not  operated  ac- 
cording to  good  standards  of  mill  practice,  but  rather  that  with  even 
the  best  of  mill  practice  there  is  a  loss  of  metals,  which  if  possible 
should  be  lessened.  Such  being  the  case,  the  problem  is  how  to  effect 
a  better  saving  of  the  valuable  minerals  than  is  now  being  made  and 
how  to  treat  the  low-grade  oxidized  ores,  which  are  not  at  all  amen- 
able to  concentration  by  the  processes  now  being  used. 

A  start  in  this  direction  has  been  made  by  the  Mines  Operating 
Co.,  which  is  treating  the  stope  fillings  of  the  Ontario  mine.  This 
oxidized  material  was  considered  as  waste  up  to  about  two  years  ago. 
The  American  Flag  mill  was  constructed  to  treat  ore  similar  to  the 
Ontario  stope  fillings,  and  the  management  contemplates  the  treating 
of  custom  ore  from  a  number  of  Park  City  and  Alta  mines. 

The  treatment  of  the  oxidized  ores  will  add  much  to  the  gold,  silver, 
and  copper  production  of  Park  City,  Alta,  and  similar  districts. 
What  was  waste  yesterday  is  a  valuable  source  of  these  metals  to-day, 
owing  to  the  application  in  a  new  way  of  an  old  process — chloridiz- 
ing,  roasting,  and  leaching — to  these  ores.  All  the  oxidized  ores  of 
this  district  contain  some  lead  and  zinc,  as  previously  stated.  In 
the  present  treatment  of  these  ores  no  zinc  is  saved  and  only  a  very 
small  part  of  the  lead.  Ofttimes  the  value  of  these  two  metals  is 
greater  than  the  gold,  silver,  and  copper  saved.  As  long  as  this  con- 
dition exists  these  ores  will  present  a  problem  well  worthy  of  all  the 
time  and  money  given  to  its  solution. 

TINTIC  DISTRICT. 

The  Tintic  district0  includes  all  the  mines  adjacent  to  Eureka, 
Knightsville,  Mammoth,  and  Silver  City.  Shipments  from  this 
district  have  continued  since  1870. 

The  Tintic  district  is  considered  as  being  a  silver-lead  district, 
although  the  ores  mined  can  be  divided  into  four  classes:  Highly 
siliceous  gold  ore,  gold-silver-lead-copper  ores,  gold-silver  lead  ores, 

a  For  a  description  of  the  geology  of  the  ore  deposits,  see  Tower,  G.  W.,  Jr.,  and  Smith, 
G.  O.,  Geology  and  mining  industry  in  the  Tintic  district:  19th  Ana.  Rept.,  1897-98, 
U.  8.  Geol.  Survey,  1899.  pp.  001-767. 


SITUATION   AND  EXTENT  OF   THE  LOW-GRADE   ORES.  15 

and  oxidized  zinc  ores  containing  small  amounts  of  silver  and  lead. 
Primary  sulphide  ore  in  any  quantity  has  not  been  encountered  in 
the  district. 

On  account  of  the  large  proportion  of  sulphide  ore  and  concen- 
trates shipped  to  the  Salt  Lake  smelters,  siliceous  ores  are  in  de- 
mand. Hence  siliceous  ores  are  shipped  from  the  Tintic  district  in 
large  quantities.  A  few  years  ago  such  siliceous  ore  was  not  con- 
sidered milling  ore  unless  the  value  of  the  metal  content  was  over  $20 
per  ton. 

The  ores  as  mined  in  the  district  consist  of  highly  siliceous  gold 
ore,  high-grade  silver-lead  ore,  siliceous  silver-lead  ore,  oxidized  zinc 
ore,  and,  rarely,  copper  ore.  In  mining  high-grade  silver-lead  ore, 
generally  the  amount  of  lower  grade  oxidized  material  encountered 
is  much  larger  than  the  amount  of  high-grade  ore  extracted. 

The  oxidized  ores  now  comprise  the  bulk  of  the  ore  shipments  from 
Tintic.  The  amount  of  sulphide  ore  mined  is  small,  most  of  it 
being  high-grade  lead  ore  varying  in  its  silver  content.  The  zinc 
ore,  for  the  greater  part,  is  encountered  in  the  development  and 
extraction  of  the  two  classes  of  silver-lead  ore,  generally  as  separate 
stopes  in  the  footwall  of  the  silver-lead  ore  or  as  linings  to  silver- 
lead  stopes.  In  addition  to  the  classes  of  ore  mentioned,  there  is 
encountered  with  them  ores  of  low  grade.  If  the  valuable  minerals 
in  this  low-grade  material  are  contained  in  scattered  lumps  of  lead 
sulphide,  or  oxidized  lead,  the  mineral  is  sorted  either  by  hand  pick- 
ing or  by  screening,  depending  on  the  fineness  of  the  pay  ore.  The 
rejected  fines  contain  gold,  silver,  copper,  and  lead  to  the  value  of 
$2  to  $8  per  ton,  with  general  averages  of  $5  to  $6  per  ton.  In  addi- 
tion to  this  class  of  material,  large  quantities  of  highly  siliceous  ore, 
of  an  average  value  of  $6  per  ton,  have  been  developed  in  the  search 
for  higher  grade  ore.  In  some  parts  of  the  district  the  siliceous  ore 
carries  chiefly  lead  and  silver,  and  in  others  it  carries  gold,  silver, 
and  lead,  or  gold,  silver,  copper,  and  lead.  Nearly  all  the  mines  con- 
tain some  siliceous  ore. 

It  is  estimated  that  the  Tintic  district  contains  at  least  2,000,000 
tons  of  low-grade  copper-lead-silver-gold  ore,  which  assays  approxi- 
mately as  follows:  Gold,  0.10  ounce  per  ton;  silver,  4  ounces;  lead, 
1  to  3  per  cent ;  copper,  0.5  per  cent. 

The  Knight-Christensen  mill,  above  Silver  City,  was  constructed 
to  treat  this  class  of  ore.  The  mill  has  a  capacity  of  approximately 
100  tons  a  day,  and  the  process  used  aims  at  effecting  a  large  saving 
of  the  gold,  silver,  and  copper.  The  lead  is  brought  into  solution, 
but  at  this  writing  little  lead  is  saved,  because  a  method  of  economi- 
cally precipitating  that  metal  has  not  yet  been  devised.  In  the 
aggregate  an  appreciable  quantity  of  lead  is  lost  in  this  manner. 
This  problem  is  receiving  considerable  attention. 


16  TREATMENT  OF   LOW-GRADE   ORES. 

Nearly  all  the  mines  in  the  Tintic  district  have  more  or  less  sine 
ore,  either  in  separate  stopes  adjoining  the  lead  stopes  or  as  shells 
in  the  lead  stopes.  The  zinc  ores  are  all  oxides  and  contain  small 
amounts  of  lead  and  silver. 

The  Yankee  Consolidated,  May  Day,  Uncle  Sam,  and  Mammoth 
mines  report  oxidized  zinc  ore  in  excess  of  200,000  tons.  The  zinc 
content  ranges  from  5  to  25  per  cent.  During  the  year  1913  a  total 
of  6,457  tons  of  zinc  ore  was  shipped.  The  average  zinc  content  was 
33.06  per  cent.  Under  present  conditions  it  does  not  pay  to  ship 
such  oxidized  ore  containing  less  than  30  per  cent  zinc,  if  the  price  of 
spelter  is  below  5.5  cents  per  pound.  The  problem  presented  here  is 
the  devising  of  a  method  for  the  treatment  of  these  low-grade  zinc 
ores;  also  for  the  extraction  of  the  zinc  contained  in  the  lead-silver 
ores  shipped. 

STOCKTON    DISTRICT. 

For  some  years  past  the  only  shippers  from  the  Stockton  district 
have  been  the  Bullion  Coalition  and  the  Ben  Harrison  mines.  The 
Ben  Harrison  ore  is  shipped  to  smelters  and  as  far  as  can  be  deter- 
mined at  this  time  (February,  1915)  no  bodies  of  low-grade  ore  of 
any  moment  have  been  encountered. 

At  the  Bullion  Coalition  mine  about  50  tons  of  silver-lead-zinc-iron 
pyrite  ore  are  treated  daily.  The  mill  is  of  the  ordinary  type  of 
lead-concentrating  plant.  The  ore  is  very  high  in  iron  sulphide.  No 
zinc  concentrate  is  made,  the  lead  being  separated  from  the  iron 
pyrite  and  zinc  without  much  difficulty.  The  concentrates  contain 
about  9  per  cent  zinc ;  the  rest  of  the  zinc  goes  into  the  tailings. 

In  the  early  operation  of  this  plant  oxidized  ores  formed  the  ma- 
jor part  of  the  material  sent  through  the  mill.  It  is  estimated  that 
the  tailings  dump  contains  approximately  175,000  tons.  About  one- 
half  of  this  quantity  is  oxidized  material.  The  balance,  forming  the 
top  layer  of  the  dump,  consists  of  lead-zinc  tailings  containing  a  high 
proportion  of  iron,  about  23  per  cent,  in  the  form  of  pyrite.  These 
tailings  have  a  gross  value,  in  gold,  silver,  lead,  and  zinc  content  of 
about  $10  per  ton.  The  zinc  is  combined  chemically  with  a  high  per- 
centage of  iron.  The  material  in  these  tailings  defies  economical 
separation  of  the  contained  lead  and  zinc  minerals  by  ordinary  meth- 
ods, except  through  the  application  of  one  or  more  processes,  such  as 
roasting,  magnetic  separation,  or  flotation,  combined  with  hydro- 
mechanical  processes. 

In  the  Stockton  district  a  large  supply  of  oxidized  zinc  ore  is  re- 
reported.  In  the  Old  Honerine  mine  the  oxidized  ore  extends  to  the 
700-foot  level;  from  the  700  to  1,300  foot  level,  the  deepest  work- 
ings, the  ore  is  a  mixture  of  lead  and  zinc  sulphides.  The  oxidized 
zinc  ore  is  of  little  value  unless  some  means  of  concentrating  it  before 


SITUATION    AND   EXTENT   OF    THE    LOW-GRADE   ORES.  17 

shipment  can  be  found.  The  zinc  in  the  lead  concentrates  is  an  eco- 
nomic loss.  Some  cheap  and  efficient  means  should  be  found  for 
treating  the  tailings  and  saving  all  the  metallic  contents. 

DRY    CANYON    AND    OPHIR    DISTRICT. 

Dry  Canyon  can  be  made  a  producer  of  low-grade  zinc  ore  if  a 
method  is  devised  for  economically  treating  the  mixed  carbonate  and 
silicate  of  zinc.  A  considerable  quantity  of  this  ore  is  found  in  the 
old  workings.  Much  more  could  probably  be  developed  if  it  were 
profitable  to  mine  low-grade  zinc  ores.  In  mining  this  low-grade 
zinc  ore  much  of  the  profit  would  undoubtedly  be  spent  in  the  devel- 
opment of  new  workings,  particularly  at  depth,  so  that  new  mines 
would  actually  be  made  from  the  profit  derived  from  material  con- 
sidered waste  at  the  present  time. 

Approximately  120  tons  of  tailings  daily  are  being  produced  in 
the  Ophir  Hill  Consolidated  mill.  According  to  the  management 
750,000  tons  of  tailings  accumulated  on  the  dumps  in  Ophir  Canyon 
during  the  past  12  years. 

These  tailings  are  said  to  assay  as  follows :  Copper,  0.65  per  cent ; 
lead,  0.74  per  cent ;  zinc,  4  to  5  per  cent ;  silver,  2.78  ounces  per  ton. 
The  concentrate  produced  from  the  crude  ore  contains  approximately 
7.5  per  cent  zinc,  for  which  the  shipper  receives  nothing. 

DEEP  CREEK  DISTRICT. 

With  the  exception  of  the  Western  Utah  mine  and  several  gold 
mines,  sufficient  development  work  has  not  been  done  in  -the  Deep 
Creek  district  to  enable  one  to  judge  whether  there  will  be  a  low- 
grade  or  complex  ore  problem.  Numerous  fissures  from  2  to  6  feet 
wade  have  been  partly  developed  throughout  the  granite  area.  Some 
rich  lead  ore  has  been  mined  at  a  number  of  places.  The  material 
on  the  dumps  is  highly  siliceous  and  the  sulphide  ores  are  an  inti- 
mate mixture  of  lead-zinc  and  iron  sulphides.  More  development 
work  will  have  to  be  done  to  prove  the  possibilities  of  this  district. 
The  treatment  of  the  gold,  bismuth,  copper,  or  silver-lead-zinc  ores, 
from  the  partly  developed  properties  presents  no  especial  difficulties, 
except  that  water  had  to  be  brought  long  distances,  and  the  district 
is  50  miles  from  a  railroad. 

MILFORD  DISTRICT. 

The  Milford  district  includes  the  Beaver,  Frisco,  Newhouse,  and 
other  properties  adjacent  to  Milford.  There  are  marked  differences 
in  the  character  of  the  different  deposits.  Ores  are  found  in  quartz- 
monzonite  which  are  similar  to  those  mined  by  the  Utah  Copper  Co. 

79474°— 15 3 


18  TREATMENT   OF    LOW-GRADE    ORES. 

at  Bingham;  ores  are  also  found  in  the  sedimentary  rocks  and  in 
volcanic  rocks. 

The  quartz-monzonite  type  of  deposit  is  represented  by  the  Cactus 
ore  zone  and  by  the  O.  K.  mine.  Both  of  these  properties  have  pro- 
duced high-grade  ore,  but  their  present  value  lies  in  the  extremely  low- 
grade  material  making  up  the  reserves  of  the  mines.  No  tonnage  is 
reported  from  the  O.  K.  propert}7.  Various  estimates  have  been  made 
on  the  amount  of  ore  in  the  Newhouse  or  Cactus  district.  The  ore  is 
a  low-grade  copper  ore  containing  approximately  1.2  per  cent  of  the 
metal.  In  the  tailings  dump  there  is  estimated  to  be  over  500,000 
tons  of  tailings  containing  more  than  4,000,000  pounds  of  copper. 

Deposits  in  the  sedimentary  rocks  are  numerous.  For  the  most 
part  the  ores  mined  from  such  deposits  in  this  district  have  been 
high  grade  and  onty  recently  have  low-grade  primary  ores  been  en- 
countered. The  operators  report  no  considerable  tonnage,  and  as 
far  as  could  be  determined  no  metallurgical  problem  presents  itself 
except  the  economic  loss  represented  by  the  zinc  contained  in  the 
lead-silver  ore  shipped,  and  the  lead  in  the  zinc  ore  shipped. 

The  same  condition  exists  in  the  mining  region  adjacent  to  Miners- 
ville  and  Beaver  City.  All  the  properties  on  which  work  is  being 
done  are  in  the  prospect  stage;  at  least  there  are  no  mines  in  the 
sense  of  having  ore  blocked  out,  except  they  be  gold  properties. 
Undoubtedly  deposits  of  commercial  value  will  be  developed  in  some 
of  the  many  old  properties  in  the  vicinity  of  Milford — ores  that  will 
be  similar  to  some  of  those  found  in  the  Park  City  and  Tintic  dis- 
tricts. 

Mineralization  in  the  igneous  or  volcanic  rocks  has  taken  place  at 
numerous  places.  There  are  two  commercially  important  mines  of 
this  type  in  this  section,  namely,  the  Horn  Silver  and  the  Beaver 
Carbonate. 

It  is  reported  that  the  Beaver  Carbonate  mine,  developed  to  the 
700-foot  level,  has  blocked  out  a  quantity  of  low-grade  silver-lead 
ore  assaying  5  to  12  ounces  of  silver  per  ton  and  6  to  10  per  cent  lead. 
A  considerable  quantity  of  material  is  represented  by  the  tailings 
•dump,  but  its  estimated  value  could  not  be  ascertained. 

According  to  the  general  manager  of  the  Horn  Silver  property, 
three  ore  problems  are  presented  at  that  mine.  These  are : 

1.  The  fillings  of  the  old  stopes,  which  consist  of  carbonate  ore 
high  in  silica  and  assaying  approximately  as  follows : 

Lead per    cent—     12.  0 

Copper do 0.  7 

Silica do 52.0 

Lime do 8.  0 

Silver ounces__       6.  0 

About  200,000  tons  of  such  material  is  in  the  stopes  down  to  the 
750-foot  level. 


SITUATION   AND  EXTENT   OF    THE   LOW-GRADE   ORES.  19' 

2.  Low-grade  sulphide  ore  left  in  the  mine  below  the  oxidized 
zone.    This  ore  assays  as  follows: 

Iron per  cent—  5.  0-6.0 

Zinc do 20.  0 

Silica do 60.0 

Lead do 10.0 

Copper do 0.5 

Silver ounces 5.0 

3.  The  old  concentrating-mill  tailings,  of  which  there  are  approxi- 
mately 190,000  tons,  reported  to  assay  about  as  follows : 

Lead per   cent-,  8.  0 

Zinc do 7.0 

Copper do 0.4 

Silica 1 do 61.  O 

Calcium  oxide do 8.  0 

Iron do 5.  0 

Sulphur do 8.  O 

Silver , ounces—  6.0 

111  1905  a  "  Peck  centrifugal  concentrator  "  mill  was  constructed  to* 
treat  these  tailings,  but  after  a  run  of  a  few  weeks  it  was  found  the 
tailings  could  not  be  treated  at  a  profit  by  this  process.  The  mill 
was  closed  down  and  nothing  has  been  done,  in  a  metallurgical  way, 
with  these  tailings  since  that  time. 

In  order  to  treat  successfully  these  ores  and  tailings  some  process 
will  have  to  be  devised  that  will  make  an  economical  saving  of  prac- 
tically all  the  valuable  metals  contained  therein.  The  fact  that  the 
tailings  are  finely  ground  adds  to  the  difficulty  of  the  problem.  A 
large  part  of  the  lead  is  in  the  sulphate  form  and  tjie  separation  of 
the  lead  and  zinc  is  difficult.  It  seems  necessary  to  devise  a  combi- 
nation of  processes  for  the  treatment  of  these  ores  and  tailings. 

SILVER   REEF   DISTRICT. 

Silver  Reef  district  is  the  name  given  to  an  area  containing  a 
series  of  silver  and  silver-copper  bearing  sandstones  in  the  central 
part  of  Washington  County,  Utah.  The  ore-bearing  beds  occur 
west,  north,  and  east  of  Leeds.  The  ores  are  confined  to  what  are 
locally  called  the  Buckeye  and  White  "  reefs."  North  of  Leeds  the 
ore-bearing  beds  dip  north ;  but  to  the  east  and  west  the  strike  and  the 
dip  changes  until,  at  points  approximately  a  mile  east  and  a  mile  west 
of  Leeds,  the  beds  strike  almost  due  south,  are  parallel,  and  dip  away 
from  a  common  axis,  forming  the  flanks  of  an  anticline.  As  far 
as  exploratory  work  has  been  done,  ore  has  been  proven  for  dis- 
tances of  approximately  1£  miles  on  the  west  flank  and  about  2  miles 
on  the  east  flank.  The  outcrops  can  be  seen  for  miles  to  the  south. 

The  ores  range  from  pure  white  sandstone,  stained  here  and  there 
with  iron  and  carrying  a  high  silver  content,  to  sandstone  colored 


20  TREATMENT   OF   LOW-GRADE    ORES. 

a  deep  blue  from  copper  and  carrying  a  high  copper  but  a  low  silver 
content. 

Men  who  have  mined  in  this  district  claim  that  the  high-grade 
silver  ore  seldom,  if  ever,  contained  copper,  and  that  as  the  copper 
content  of  an  ore  increased  the  silver  content  decreased. 

There  are  other  beds  that  are  slightly  mineralized,  but  the  inner 
or  Buckeye  Reef  and  outer  or  White  Reef  are  the  only  productive 
ones.  These  two  reefs  are  separated  by  several  hundred  feet  of 
gypsum-bearing  red  beds.  Both  underlie  the  massive  red  sandstone 
which  outcrops  about  a  mile  west  of  Leeds  as  a  bold,  vertical  cliff 
400  or  500  feet  in  height. 

No  effort  to  extract  copper  was  made  in  the  treatment  of  the 
Silver  Reef  ores.  Neither  was  the  treatment  of  silver  ores  contain- 
ing less  than  14  ounces  per  ton  undertaken.  Ores  of  this  value  con- 
taining appreciable  amounts  of  copper  were  not  treated. 

Thus,  in  the  Silver  Reef  district  there  are  low-grade  silver  ores 
and  also  copper-silver  ores.  No  work  was  done  to  determine  the 
depth  to  which  the  ore  may  extend;  when  water  was  encountered 
work  was  stopped.  The  maximum  dip  of  the  "reefs"  appears  to 
be  about  35°,  but  the  dip  is  generally  less.  The  deepest  workings 
were  in  650  feet  from  the  outcrop. 

There  undoubtedly  is  a  large  amount  of  low-grade  silver-copper 
as  well  as  low-grade  silver  ore  in  this  district.  There  is  consider- 
able virgin  ground,  and  dumps  containing  a  considerable  amount  of 
silver-copper  ore  that  justifies  attempts  at  treatment. 

Silver  Reef  is  75  miles  from  a  railroad;  water  is  plentiful,  but 
fuel  is  costly.  If  this  ore  were  treated  by  the  Holt  process — chlorid- 
izing,  roasting,  and  leaching — the  costs  would  be  too  high,  owing 
to  the  long  haul  on  the  coal  and  the  chemicals  necessary.  For  treat- 
ing these  ores  a  method  would  have  to  be  devised  which  would  use 
products  to  be  had  at  low  cost  in  the  district.  This  would  necessi- 
tate a  study  of  the  local  natural  resources  in  order  to  determine  the 
presence  of  such  necessary  products. 

Crude  oil  has  been  found  near  by  in  sufficient  quantity,  and  filings 
have  been  made  on  water-power  sites  on  the  Virgin  River. 

EASTERN   UTAH. 

Copper  ores  in  sandstone  are  to  be  found  in  eastern  Utah  from 
the  Uintah  Mountains  to  the  Arizona  boundary  line.  Few  of  these 
copper  showings  are  of  any  economic  importance.  The  erratic  oc- 
currence in  eastern  Utah  of  these  copper  ores  in  sandstone  is  a  feature 
that  tends  to  hinder  their  exploitation.  The  principal  obstacles  to 
their  development  are  as  follows:  Variable  copper  content,  distance 
from  railroads,  lack  of  water,  and  in  most  cases  the  smallness  of  the 


CHEMICAL   CHARACTERISTICS   OF    THE   UTAH   ORES. 


21 


deposit.  If  the  copper  content  is  high  the  deposit  is  small;  if  the 
deposit  is  large  the  copper  content  is  variable.  A  large  supply  of 
ore  of  uniform  grade  is  necessary  if  low-grade  ore  is  to  be  mined  at  a 
profit.  Cheap  mining  calls  for  a  large  tonnage.  A  number  of  dis- 
connected lenses  of  ore  have  to  be  considered  as  a  whole,  and  the  de- 
velopment of  one  lens  lends  little  or  no  value  to  an  adjoining  lens 
as  far  as  the  blocking  out  of  the  ore  is  concerned.  Such  a  condition 
does  not  permit  cheap  mining,  especially  if  the  copper  is  scattered 
irregularly  through  the  mass. 

CHEMICAL  CHARACTERISTICS  OF   THE   UTAH  ORES. 

liy  O.  C.  RALSTON. 
RESULTS  OF  ANALYSES. 

The  results  of  analyses  of  samples  of  complex  and  low-grade  ores 
collected  in  connection  with  this  investigation  that  seem  to  present 
distinct  metallurgical  problems  are  given  in  the  table  following. 
Ordinary  free-milling  or  cyaniding  gold  ore,  for  instance,  has  not 
been  investigated,  as  the  treatment  of  such  ore  involves  no  special 
difficulties.  But  an  oxidized  ore  carrying  copper,  gold,  and  silver 
in  such  amounts  that  there  is  too  much  copper  to  allow  cyanidation 
or  amalgamation,  and  too  little  copper,  gold,  and  silver  to  be  worth 
smelting,  offers  a  distinct  metallurgical  problem.  The  follpwing 
table  of  analyses  represents  samples  of  ores  which  so  far  have  largely 
defied  economical  treatment. 

Results  of  awtliwx  of  low-grade  and  complex  ores. 

[Analysts:  L.  F.  Pattison,  W.  G.  Woolf,  O.  H.  Pierce,  A.  E.  Gartside,  C.  Y.  Pfoutz,  H.  J.  Morgan,  R.  M. 

Isham,  and  O.  C.  Ralston.] 


0 

|l 

SiOj. 

CaO. 

Fe. 

Al,03. 

MgO. 

Mn. 

As. 

S. 

C02. 

Zn. 

Pb. 

Cu. 

Ag. 

Au. 

Bi. 

1 

P.ct. 
12.9 

P.ct. 
9.75 

P.ct. 
7.56 

P.  ct. 
6.2 

P.ct. 

P.ct. 

P.  ct. 

P.ct. 
0.20 

P.ct. 
15.90 

P.ct. 
20.49 

P.ct. 

8.65 

P.ct. 

Oz.p.t. 
0.45 

o^.t. 

P.ct. 

2 

10  6 

8.20 

33.00 

3.3 

13.19 

8.6 

.77 

.28 

Tr. 

3 

8  5 

12  42 

18  50 

2  6 

23  57 

18  2 

0  1 

16 

4 

60  4 

2.67 

16.25 

7.6 

.40 

1.81 

.87 

9.02 

.1 

1.32 

Tr. 

5 

58  3 

3  67 

17  17 

1  6 

0  4 

.74 

4  77 

.58 

7 

3  75 

0  09 

6 

81.2 

.74 

10.12 

.9 

.17 

.78 

.4 

5.53 

.08 

7 

94  1 

82 

2  14 

.6 

37 

.58 

.1 

5  30 

.18 

8 

69.0 

2.45 

13.08 

12.8 

2.60 

.58 

.05 

1.04 

7.06 

.25 

9 

69  5 

2.56 

8.38 

2.7 

6.18 

.97 

1.22 

3  15 

.23 

10 

52.7 

2.30 

11.75 

5.8 

6.50 

2.12 

7.80 

1.1 

Tr. 

1.80 

.03 

11 

80.8 

.57 

4.19 

7 

1.05 

.50 

5.5 

7.90 

.08 

12 

81  9 

1  39 

4  50 

Tr. 

22 

52 

50 

4  3 

2  80 

03 

13 

31.4 

10.25 

4.19 

Tr. 

.65 

19.84 

15.7 

.55 

.30 

.23 

14 

51  3 

4.90 

12.47 

8.0 

1.7 

7.40 

1.3 

3.5 

Tr. 

9  55 

.04 

15 

76.6 

2.05 

5.72 

3.6 

2.29 

1.8 

.3 

.75 

6.71 

.13 

16 

17 

59.6 

.50 

15.53 

4.7 

.07 

.6 

2.3 

.2 
1  02 

4.42 
10 

.05 
Tr 

18 

.87 

Tr. 

19 

1.57 

.10 

20 

2  47 

20 

21 

.35 

22 

2  82 

.1 

23 

15  0 

2 

?4 

.6 

25 

95.0 

1.00 

.50 

2.1 

Tr. 

10.48 

22  TREATMENT   OF   LOW-GRADE   ORES. 

Results  of  analyses  of  law-grade  ami  complex  ores — Continued. 


® 

¥ 

Si02. 

CaO. 

Fe. 

A1203. 

MgO. 

Mn. 

As. 

S. 

C02. 

Zn. 

Pb. 

Cu. 

Ag. 

Au. 

Bi. 

26 

P.ct. 

P.ct. 

P.ct. 

P.ct. 

P.ct. 

P.ct. 

P.ct. 

P.ct. 

P.ct. 

P.ct. 

P.ct. 

P.ct. 
0.1 

Oz.  p.  t. 

Oz.  p.  t. 

P.ct. 

?7 

.00 

2  1 

12  18 

Tr 

7» 

.50 

7 

6  2 

29 

60 

g 

7  68 

30 

1  .00 

8 

2  50 

31 

.00 

8 

6  40 

33 

.00 

3.3 

10  32 

33 

J.50 

9 

22 

34 

.80 

1.6 

92 

35 

.40 

2  7 

3  68 

36 

.60 

4 

2  68 

37 

1.3 

1.1 

2  00 

0  03 

38 

1.9 

4 

14  24 

39 

13  8 

1  4 

2  76 

01 

40 

41 

21 

19 

0  94 

4? 

1  41 

43 

2  53 

44 

09 

45 

70 

06 

3  17 

46 

47 

38.2 

1.43 

16.35 

4.2 

19.70 

6.8 

6.9 

.(5 

40  59 

.07 

48 

49.2 

21.45 

6.70 

2.2 

18.  87 

1.02 

.20 

.04 

49 

30.8 

10.05 

2.25 

7.4 

0.46 

12.70 

10.55 

16.88 

14.87 

.72 

29.56 

.01 

50 

22.0 

5.05 

16.35 

1.85 

.20 

24.75 

6.48 

12.0 

15.39 

.07 

4.86 

.04 

51 

43.3 

3.20 

5.30 

21.6 

.97 

3.15 

2.33 

5.37 

16.54 

.62 

17.90 

.01 

52 

57.4 

10.73 

1.18 

1.5 

1.87 

1.90 

21.71 

3.32 

2.00 

.07 

4.66 

.02 

53 
54 

73.9 
10.5 

4.68 
2.10 

1.12 
33.00 

4.4 
7.6 

.37 

i.13 

.18 
37.34 

5.24 

6.93 
4.4 

4.16 
3.00 

.11 
.10 

15.94 

.78 

.18 
.01 

55 

9  3 

3  40 

28  8 

15  8 

2  33 

35  86 

8  5 

10  47 

07 

2  43 

.02 

66 

14.0 

2.10 

1.69 

33.26 

11.4 

2.59 

.06 

1.06 

.01 

57 

12.5 

1.10 

15.00 

8.6 

.92 

19.04 

29.9 

.21 

.13 

.15 

Tr. 

58 

18.0 

1.10 

22.2 

14.6 

2.42 

30.32 

13.1 

10.56 

.10 

2.65 

.02 

59 

3.00 

60 

53.6 

2.20 

4.4 

8.5 

.37 

6.13 

1.37 

6.3 

7.4 

.25 

6.7 

.02 

TYPES  OF  ORES  ANALYZED. 

The  ores  represented  in  the  table  of  analyses  may  be  considered  as 
a  number  of  distinct  types  classifiable  on  the  basis  of  chemical  com- 
position, mineralogical  constituents,  as  shown  by  microscopic  ex- 
amination; on  information  in  the  geological  reports  on  these  ores; 
on  the  action  of  dilute  acids  on  the  ores;  and  also  on  the  history  of 
metallurgical  failures  in  treating  these  ores.  Eight  types  of  com- 
ple  or  low-grade  ores  may  be  distinguished,  as  follows : 

1.  Copper  carbonate  ores. 

2.  Oxidized  ores  carrying  lead  carbonate  and  silver.     Samples  4, 
11,  12,  and  14  represent  this  class.     In  a  number  of  places  attempts 
have  been  made  to  concentrate  such  ores,  but  much  of  the  lead  car- 
bonate was  lost  in  the  tailings  on  account  of  the  habit  of  that  mineral 
to  divide  into  small  flakes  which  tend  to  float  off.     Most  of  the  ores 
contain  over  50  per  cent  of  insoluble  material,  but  the  amount  of 
soluble  iron  and  lime  presents  some  difficulties  to  the  application  of 
hydrometallurgical   processes.     Analyses   indicate   that   these   ores, 
however,  are  markedly  similar  in  composition   (except  for  lack  of 
copper)  to  the  ore  from  the  old  Ontario  stopes  now  being  treated 
by  the  Mines  Operating  Co.  at  Park  City,  Utah. 


CHEMICAL   CHARACTERISTICS   OF   THE   UTAH   ORES.  23 

3.  Oxidized  ores  carrying  small  amounts  of  copper  and  lead  as 
carbonates  and  also  gold  and  silver.     Samples  5,  6,  7,  8,  9,  and  15 
are  representative  of  this  class.     As  stated,  this  type  of  ore  has  not 
enough  total  value  to  make  profitable  at  present  its  direct  shipment 
to  the  smelter,  and  the  presence  of  oxidized  copper  minerals  render 
unprofitable  the  extraction  of  the  gold  and  silver  cyanide  or  amalga- 
mate.    Most  of  these  ores  are  siliceous,  but  some  of  them  show  by 
analysis  high  content  of  lime  and  iron  and  might  be  classed  as  basic 
ores. 

4.  Oxidized  ores  with  zinc  as  the  chief  constituent,  and  carrying 
occasionally  gold  and  silver.     This  type  of  ore  is  represented  by 
samples  2,  3,  and  13.     Most  of  these  ores  do  not  contain  enough  zinc 
to  be  accepted  by  the  zinc  smelters,  and  the  oxidized  zinc  minerals 
present  frustrate  attempts  to  recover  the  gold  and  silver  alone.     The 
zinc  content  is  too  high  to  allow  smelting  in  a  lead  or  copper  blast 
furnace.     An  oxidized  ore  in  which  zinc  is  the  only  valuable  con- 
stituent must  contain  at  least  30  per  cent  of  zinc  to  be  accepted  by 
the  zinc  smelter,  although  some  shipments  of  ore  containing  22J  per 
cent  were  made  with  spelter  at  7  cents  a  pound,  but  none  of  the  sam- 
ples showr  even  22  per  cent  of  zinc. 

5.  Oxidized  ores  with  zinc  and  lead  as  the  two  chief  valuable  con- 
stituents, and  occasionally  carrying  some  silver  and  gold.     This  type 
of  ore  is  represented  by  samples  1,  10,  52,  and  53.     In  general,  such 
ores  contain  too  much  zinc  to  allow  smelting  in  a  lead  furnace  and 
too  much  lead  to  allow  smelting  in  a  zinc  retort.     Moreover,  the 
oxidized  condition  of  the  ores  does  not  permit  clean  mechanical 
separation  of  the  lead  and  the  zinc  minerals. 

6.  Oxidized  ore  containing  zinc,  lead,  copper,  gold,  and  silver. 
There  is  some  of  this  type  of  ore  in  nearly  all  of  the  Tintic  district 
mines,  in  the  Horn  Silver  mine  of  the  Milford  district,  and  in  the 
Park  City  mines.     It  is  both  low  grade  and  complex,  and  it  might 
be  well  to  observe  here  that  the  "  complexity  "  is  generally  due  either 
to  the  presence  of  zinc  or  to  the  oxidized  condition  of  the  ore.     It  is 
practically  impossible  to  separate  mechanically  the  different  mineral 
constituents  of  oxidized  ores. 

7.  Any  of  the  above  groups  only  partly  oxidized.     Examples  of 
such  ores  are  samples  3,  51,  and  the  copper  ores  of  the  Utah  Copper 
Co.     Such  ores  call  for  two  kinds  of  treatment,  namely,  one  for 
the  sulphide  minerals  and  one  for  the  oxidized  minerals,  hence  the 
complexity  of  this  group. 

8.  Complex  sulphides  of  zinc,  lead,  copper,  and  iron  carrying  silver 
and  gold.     These  ores,  which  are  represented  by  samples  47, 49, 50, 51, 
54,  55,  56,  and  58,  are  of  common  occurrence.     As  a  rule  the  presence 
of  zinc  is  the  complicating  factor,  as  a  penalty  is  exacted  by  the  lead 
and  copper  smelters  if  the  zinc  content  is  above  a  certain  percentage. 


24  TREATMENT   OF    LOW-GRADE    ORES. 

Improvements  in  the  methods  of  treating  complex  sulphide  ores  of 
this  class  are  much  to  be  desired  in  order  that  losses  of  zinc  and  lead 
may  be  avoided  or  turned  into  profits. 

It  may  be  said  that  the  main  metallurgical  problem  in  Utah  is 
to  find  processes  which  can  successfuly  and  economically  treat  great 
amounts  of  low-grade  oxidized  ores.  Utah  probably  has  more  than 
an  average  share  of  such  ores.  There  are,  for  instance,  few  large 
mining  districts  known  in  which  the  zone  of  oxidization  extends  so 
deeply  as  it  does  in  the  Tintic  district.  The  oxidized  minerals  are, 
as  a  rule,  soft  and  of  lower  specific  gravity  than  the  corresponding 
sulphides,  and  often  are  so  intermixed  as  almost  to  defy  any  known 
kind  of  mechanical  separation.  On  such  ores  as  these,  wet  chemical 
processes  should  be  the  first  ones  to  be  considered,  with  the  possible 
exception  of  the  oxidized  zinc  ores.  There  seems  to  be  a  possibility 
of  successfully  treating  the  latter  with  certain  forms  of  "igneous 
concentration.'' 

METALLURGICAL  TREATMENT  OF  THE  ORES. 

By  D.  A.  LYON,  R.  H.  BRADFORD,  S.  S.  ARENTZ,  O.  C.  RALSTON,  and  C.  L.  LARSON. 

PROCESSES  OF  TREATMENT. 

OXIDIZED  ORES. 

The  present  practice  in  the  State  as  regards  ores  of  type  2 — those 
carrying  lead  carbonate  and  silver — is  to  recover  all  that  can  be  re- 
covered by  ordinary  methods  of  gravity  concentration  and  to  allow 
any  flaky  lead  carbonate  carried  over  to  go  into  the  tailings.  The 
recovered  lead  carbonate  is  shipped  to  the  smelter. 

The  Holt-Dern  process  at  Park  City  and  the  Knight- Christensen 
process  at  Tintic  were  evolved  for  the  treatment  of  ores  of  type  3. 
In  these  processes  the  ore  is  roasted  with  salt  and  the  metals  leached 
out  with  acid  brine  solution. 

The  ores  of  type  4.  carrying  oxidized  zinc  minerals  as  the  chief 
constituent  and  occasionally  some  gold  and  silver,  are  not  concen- 
trated in  any  manner  whatever  at  present,  except  by  hand  sorting  at 
the  mine.  These  ores  must  be  of  smelting  grade  to  be  of  any  value. 
The  zinc  smelters  require  a  zinc  content  of  at  least  25  per  cent  in  the 
ore  shipped  to  them.  Moreover,  as  the  zinc  smelters  are  all  at  some 
distance,  it  is  easily  seen  that  in  order  to  make  an  ore  of  this  kind 
yield  the  miner  a  profit  at  present  it  must  run  well  over  30  per  cent 
in  metallic  zinc.  On  that  account  there  is  not  a  very  great  tonnage 
of  ores  containing  less  than  30  per  cent  of  zinc  marketed.  The  greater 
part  goes  to  the  dumps  or  is  stored  in  the  old  stopes  of  the  mines. 

The  ores  of  type  5,  carrying  both  oxidized  lead  and  zinc  minerals, 
with  gold  and  silver  are  in  some  instances  being  concentrated. 
Whatever  heavy  lead  carbonate  and  silver  can  be  concentrated  out  by 


METALLURGICAL  TREATMENT  OP   THE   ORES.  25 

gravity  methods  is  saved,  leaving  the  zinc  and  considerable  lead  and 
silver  in  the  tailings.  These  zinc  tailings  are  sometimes  shipped  to 
zinc  smelters.  When  the  zinc  content  is  low  enough  (below  10  per 
cent)  they  are  sometimes  shipped  direct  to  a  lead  or  copper  smelter. 

The  ores  of  type  6,  carrying  oxidized  zinc,  lead,  and  copper  min- 
erals with  silver  and  gold,  also  present  a  rather  serious  problem. 
At  present  the  object  sought  in  milling  these  ores  is  to  get  rid  of 
the  zinc  entirely.  Zinc  is  a  detriment  in  the  metallurgy  of  most  other 
metals,  and  ores  of  high  gross  value  often  lie  useless  on  account  of 
the  difficulty  of  separating  the  zinc  from  the  other  mineral  constitu- 
ents. Only  those  ores  in  which  the  zinc  content  is  so  low  that  it 
will  not  interfere  with  smelting  the  other  metals  are  shipped. 

In  the  ores  of  type  7,  which  are  partly  oxidized,  the  heavy  sul- 
phides can  be  recovered  by  ordinary  gravity  concentration  methods, 
or  by  flotation.  The  only  loss  is  in  the  oxidized  minerals,  with  the 
exception  of  the  lead  carbonate,  part  of  which  is  also  recovered.  As 
previously  stated,  the  Utah  Copper  Co.  in  working  its  ores  recovers 
the  sulphides,  but  not  the  oxides.  However,  the  company  is  planning 
to  leach  the  tailings  dumps  later  to  recover  the  oxides. 

COMPLEX  SULPHIDE  ORES. 

The  ores  of  type  8,  complex  sulphide  ores,  have  been  encountered 
in  those  camps  where  the  mines  have  reached  the  sulphide  zone.  At 
Bingham  this  class  of  ores  is  being  successfully  treated  in  one  in- 
stance by  wret  concentration  followed  by  drying  and  electrostatic  sep- 
aration, as  practiced  in  the  United  States  mill  at  Midvale. 

At  Park  City  mixed  sulphides  have  been  treated,  at  the  Daly  Judge 
mill,  by  wet  concentration,  followed  by  drying,  very  close  sizing,  and 
pneumatic  separation.  The  mixed  sulphides  from  another  mine 
were  treated  by  wet  concentration,  followed  by  light  roasting  and 
electromagnetic  separation. 

Smelting  mixed  sulphide  ores  in  a  lead  or  copper  blast  furnace  is 
practical  only  when  the  zinc  content  of  the  ore  is  less  than  10  per 
cent.  When  such  ores  are  concentrated,  the  object  is  to  obtain  a  rich 
concentrate  with  less  than  10  per  cent  of  zinc.  This  concentrate 
can  then  be  sold  to  the  local  smelters,  and  the  zinc  middlings  can  be 
treated  as  described  above,  or  else  sent  to  the  "  blowing  up  "  furnace 
to  be  made  into  paint  pigment. 

The  application  of  dry  chlorination  processes  to  complex  sulphide 
ores  is  under  experiment  on  a  commercial  scale  at  Kellogg,  Idaho, 
and  at  Helena,  Mont.  The  sulphides  are  chloridized  by  heating  in 
contact  with  chlorine  gas.  The  metals  other  than  zinc  are  extracted 
by  leaching  and  deposition.  The  zinc  chloride  is  concentrated,  com- 
pletely dried,  and  fused  ready  for  the  electrolytic  cell.  The  results 
of  these  tests  are  awaited  with  interest. 


26  TREATMENT  OF   LOW-GRADE   ORES. 

Finally,  the  complex  sulphide  ores  are  also  being  treated  by  grav- 
ity concentration  as  well  as  by  the  use  of  electrostatic  and  magnetic 
concentrating  machines. 

REMOVAL  OF  COPPER. 

In  those  ores  in  which  copper  is  a  cause  of  complications  in  the 
metallurgical  treatment  there,  seems  now  to  be  a  fairly  good  assur- 
ance that  it  can  be  removed  economically.  At  many  localities  in  the 
United  States  the  problem  is  being  solved  more  or  less  successfully. 
On  that  account  the  work  of  the  present  investigation  is  lightened  to 
some  extent  because  only  the  most  promising  methods  need  be  tried 
on  the  Utah  ores.  As  regards  the  treatment  of  zincky  oxidized  ores, 
that  is  a  more  difficult  problem.  The  investigation  by  the  metallur- 
gical research  department  of  the  State  School  of  Mines  has  included 
keeping  in  touch  with  the  work  of  IT  different  concerns  that  are 
trying  to  solve  practically  the  same  problem.  Much  pioneer  work 
remains  to  be  done. 

CHIEF   METALLURGICAL,  PROBLEMS. 

Summing  up,  then,  one  may  say  that  although  many  problems 
present  themselves  to  those  who  are  attempting  to  devise  processes 
for  economically  treating  the  low-grade  and  complex  ores  of  Utah, 
the  following  seem  to  be  the  most  difficult : 

TREATMENT  OF   OXIDE   AND   CARBONATE  ORES. 

The  waiters  know  of  no  commercially  successful  process  whereby 
the  valuable  minerals  may  be  concentrated  out  of  the  low-grade 
oxidized  ores.  As  smelting  processes  are,  for  the  most  part,  appli- 
cable only  to  the  treatment  of  materials  in  which  the  values  are  more 
or  less  concentrated,  it  follows  that,  for  the  present  at  least,  only 
hydrometallurgical  processes  are  suited  to  the  treatment  of  low- 
grade  ores  in  which  the  metals  are  present  as  oxides  or  as  carbonates. 
The  problem  is,  therefore,  to  devise,  if  possible,  hydrometallurgical 
processes  that  can  successfully  and  economically  treat  low-grade  oxi- 
dized and  carbonate  ores. 

TREATMENT   OF   ZINC-BEARING    ORES. 

At  present  none  of  the  concentrating  processes  employed  effect  as 
close  a  separation  of  the  zinc  and  lead  in  complex  sulphide  ores  as 
is  desirable,  as  is  shown  in  the  table  following,  taken  from  a  paper  a 

•Lyon,  D.  A.,  and  Arentz,  S.  S.,  Losses  of  zthe  in  mining,  milling,  and  smelting: 
Bull.  91,  Am.  Inst  Min.  Eng.,  July,  1914,  pp.  1422-1423. 


METALLURGICAL  TREATMENT  OP   THE   ORES. 


27 


by  Lyon  and  Arentz,  which  was  presented  at  the  Salt  Lake  meeting 
of  the  American  Institute  of  Mining  Engineers  in  August,  1914: 

Recovery  of  zinc  by  various  concentration  processes. 


Process. 

Zinc  in 
zinc  con- 
centrate. 

Zinc  in 
product 
going  to 
blast 
furnace. 

Proportion  of  metal  recovered. 

Zinc. 

Lead. 

Silver. 

Ordinary  wet  concentration: 
1  'ark  City,  Utah                                    

Per  cent. 

Per  cent. 

Per  cent. 
50.0 
66.0 
25.0 
065.4 

Per  cent. 
95.0 
92.0 
90.0 

Per  cent. 
75-80.0 
78.0 
85.0 

Do 

Burke,  Idaho 

Joplin  Mo 

\Vetherill  magnetic  a 

50.0 

48.0-50.0 
41.3 
49.3 

5.  0-7.  0 

10.0 
12.6 
8.6 

Huff,  electrostatic:  b 
Mitl  vale  Utah 

Eureka  Colo 

Potter  Delprat  c 

66.2 

38.5 

50.9 

De  Bavay:  d 
1910 

48.1 
48.4 
49.2 
46.0 

11.7 
14.2 
16.6 
15.84 

1911 

1912 

Mineral  separation 

85.4 

74.8 

80.1 

48.7 

10.2 

Hyde  process: 
Butte  / 

88.1 
86.4 

83.4 
80.0 

Superior  /                          ... 

62.5 

a  Editorial,  Magnetic  separation  of  zinc  blende  at  Denver,  Colo.:  Eng.  and  Min.  Jour.,  vol.  74,  August 
16,  1902,  p.  217. 

&  MacGregor,  F.  S.,  Progress  in  electrostatic  ore  dressing:  Trans.  Am.  Electrochem.  Soc.,  vol.  24, 1913, 
p.  352. 

c  Hoover,  T.  J.,  Concentrating  ores  by  flotation  (London),  1912,  p.  91, 

d  Hoover,  T.  J. ,  op.  cit.,  p.  97. 

«  Hoover,  T.  J.,  op.  cit.,  p.  105. 

/  Results  are  for  1913. 

g  About. 

The  following  extract  is  from  the  same  paper : 

In  presenting  these  facts  as  regards  the  methods  which  are  used  for  concen- 
trating zinc  ores,  we  do  not  wish  to  be  understood  as  criticizing  any  of  the 
concentration  processes  mentioned,  as  they  do  the  work  for  which  they  are 
installed,  namely,  to  separate  gold-silver-lead-copper-zinc-bearing  ores  into  two 
products,  one  of  which  shall  contain  enough  zinc  to  enable  it  to  be  profitably 
treated  by  the  zinc  smelter,  and  the  other  no  more  than  will  permit  of  its  being 
satisfactorily  treated  in  a  copper  or  lead  blast  furnace.  As  is  well  known,  in 
such  furnaces,  if  the  zinc  content  of  the  ore  constituting  the  charge  is  not 
greater  than  10  per  cent,  it  can  be  gotten  rid  of  in  the  slag  and  fumes.  The 
loss  of  this  amount  of  zinc  is,  of  course,  a  distinct  waste.  As  to  the  amount 
of  zinc  lost  in  this  manner,  the  following  example  will  serve  to  illustrate  the 
same. 

If  we  treat  ore  containing,  say,  28  per  cent  of  zinc,  we  separate  this  into  two 
products,  one  of  which  will  contain,  say,  50  per  cent  zinc,  whereas  the  other 
will  contain  most  of  the  gold,  silver,  copper,  and  lead  and  about  10  per  cent 
of  zinc.  In  other  words,  of  our  original  product  of  50  tons  we  will  have  28 
tons  (more  or  less,  dependent  upon  the  percentage  of  iron  present)  of  product 
containing  50  per  cent  zinc,  and  22  tons  containing  10  per  cent,  and,  in  addition, 
most  of  the  gold,  silver,  copper,  and  lead  contained  in  the  original  product. 
This  latter  product  goes  to  the  blast  furnace  and  ordinarily  the  zinc  content 
is  not  saved,  but  is  lost  in  the  fume  and  slag.  This  amount  of  zinc  therefore 


28  TREATMENT   OF   LOW-GRADE   ORES. 

represents  a  loss  of  almost  1,500,000  pounds  a  year.  Moreover,  this  zinc  is  lost 
for  all  time,  as  it  can  not  be  recovered,  and  when  we  consider  that  this  is  lost 
from  the  treatment  of  only  50  tons  of  concentrates  per  day,  we  can  readily  un- 
derstand, as  has  been  shown  by  those  who  have  investigated  this  subject,  that 
the  zinc  lost  in  this  wray  amounts  in  the  aggregate  to  thousands  of  tons  annu- 
ally, and,  as  has  been  pointed  out  by  Clevenger  °  and  others,  in  the  inability 
to  recover  this  zinc  lies  one  of  the  greatest  weaknesses  of  our  present-day 
metallurgical  practice,  in  that  the  zinc  so  lost  represents  a  distinct  economic 
waste,  much  of  which  will  never  be  recovered,  and  that  we  must  look  to  the 
prevention  of  this  waste  as  one  of  the  sources  from  which  we  shall  in  the 
future  obtain  a  large  part  of  our  zinc  supply. 

The  same  thing  is  of  course  true  to  some  extent  of  lead,  for  in  copper  smelt- 
ing, if  lead  is  present,  it  is  volatilized  and  no  attempt  is  made  to  recover  it, 
and  so  the  lead  is  completely  lost.  As  before  stated,  these  facts  are  not  pre- 
sented with  the  idea  of  bringing  an  indictment  against  electromechanical 
methods  of  concentration,  or  against  modern  methods  of  copper  and  lead 
smelting,  but  rather  to  emphasize  the  fact  that  although  mechanical  methods 
of  concentration  and  modern  methods  of  smelting  have  reached  a  very  high  stage 
of  development,  their  use  nevertheless  entails  a  very  great  loss  of  zinc,  which 
is  not  recoverable,  and  that  therefore  it  is  quite  likely  that  in  the  future  it  will 
be  necessary  to  stop  these  wastes  in  order  to  add  to  the  available  supply  of 
zinc. 

The  problem  therefore  which  presents  itself  is  to  derive  processes  which 
will  successfully  treat  low-grade  and  complex  ores  containing  zinc. 

CHLOBIDIZING  PROCESSES. 

The  devising  of  practicable  processes  for  treating  the  low-grade 
and  complex  ores  of  Utah  has  already  been  given  considerable  time 
and  attention  by  various  investigators  and  experimenters.  As  a 
result  of  such  work  at  least  two  chloridizing  processes  are  being  tried 
out,  one  of  which  is  known  as  the  Holt-Dern  process,  and  the  other 
the  Knight-Christensen  process. 

HOLT-DERN    PROCESS. 

The  Holt-Dern  chloridizing  process  was  discussed  by  Holt6  in  a 
paper  before  the  August,  1914,  meeting  of  the  American  Institute 
of  Mining  Engineers  at  Salt  Lake  City.  This  discussion  has  been 
reprinted  in  the  mining  journals  and  is  doubtless  available  to  those 
who  may  desire  to  acquaint  themselves  with  the  details  of  the  process 
as  applied  at  the  plant  of  the  Mines  Operating  Co.,  at  Park  City. 

F.  S.  Schmidt c  has  also  discussed  this  plant  and  personal  tests 
made  at  it,  together  with  operating  costs. 

•  Discussion  by  Clevenger,  G.  II.,  and  others,  Is  there  a  complex-ore  problem  ?  :  Met. 
and  Chem.  Eng.,  vol.  12,  May,  1914,  p.  299. 

6  Holt,  T.  I'.,  Chloridizing  leaching  at  Park  City:  Bull.  91,  Am.  Inst.  Min.  Eng.,  1914, 
pp.  1699-1708. 

"Schmidt,  F.  S.,  Rejuvenating  the  chloridizing  roast:  Min.  Sci.  Press,  Aug.  29,  19 M, 
pp.  324-328. 


METALLURGICAL   TREATMENT  OF   THE   ORES.  29 

PRINCIPAL    FEATURES    OF    PROCESS. 

Following  is  a  brief  summary  of  the  steps  in  the  process.  The  ore 
is  ground  to  8  to  10  mesh  size,  mixed  with  7J  per  cent  of  salt,  2J  per 
cent  of  coal  dust,  and  just  enough  water  to  ball  up  the  mixture.  This 
pulp  is  then  given  a  chloridizing  roast  in  air-blast  shaft  furnaces. 
The  roasted  material  is  leached  with  a  brine  solution  containing  up  to 
0.5  per  cent  of  sulphuric  acid.  The  leach  solution  is  passed  first  over 
scrap  copper  to  precipitate  the  silver,  and  then  through  a  long  series 
of  iron  boxes.  The  first  of  these  boxes  catches  fine  copper,  the  lower 
ones  produce  a  copper-lead  product.  From  90  to  95  per  cent  of  the 
silver  and  copper  are  reported  to  be  recovered  by  the  process  out- 
lined above,  and  also  about  50  per  cent  of  the  gold.  Should  the  gold 
content  be  sufficient  to  warrant  the  addition  of  bleach  to  the  pulp 
over  90  per  cent  of  the  total  gold  content  may  be  recovered. 

FACTORS  AFFECTING  THE  PROCESS. 

The  composition  and  the  other  pertinent  characteristics  of  the  ore 
that  must  be  considered  in  the  application  of  this  process  to  any 
particular  ore  will  now  be  discussed. 

The  results  of  tests  at  Park  City,  and  also  of  many  other  tests 
in  various  parts  of  the  country  strongly  indicate  successful  extraction 
of  the  gold,  silver,  and  copper  contents  of  low-grade  ores,  provided 
that  other  factors,  which  are  considered  below,  do  not  prohibit  the 
operation  of  the  process. 

A  quartz  or  porphyry  gangue  is  indifferent  to  the  reactions  that 
take  place  in  chloridizing,  and  therefore  ores  high  in  silica  are  espe- 
cially desirable.  A  limestone  gangue  or  one  of  dolomite  or  other  mag- 
nesium compounds  takes  such  active  part  in  the  reactions  that  ores 
with  such  gangues  may  or  may  not  be  amenable  to  chloridizing 
methods. 

Limestone  is  detrimental  both  in  the  roasting  and  in  the  leaching. 
In  the  roasting,  calcium  oxide  decomposes  the  metallic  salts  and  also 
silver  chloride,  thus  preventing  complete  chloridization  of  the  metal 
contents.  In  the  leaching,  any  undecomposed  lime  reacts  with  the 
acid,  thus  weakening  the  solvent  power  of  the  leaching  solution,  for 
the  solvent  action  of  the  brine  depends  on  the  presence  of  a  small 
amount  of  free  acid.  However,  should  sulphur  be  present  in  the 
ore  or  be  added,  in  quantity  sufficient  to  convert  the  lime,  during 
the  roasting  period,  to  chloride  or  sulphate,  a  good  chloridization  of 
silver  and  copper  may  be  obtained.  In  one  test  an  ore  containing 
23  per  cent  lime  was  successfully  treated  by  roasting  with  an  addi- 
tion of  12  per  cent  pyrite  and  10  per  cent  salt.  This  might  be  taken 
to  indicate  that  the  content  of  lime  need  be  limited  by  economic 
considerations  only,  the  maximum  allowable  percentage  of  lime  be- 


30  TREATMENT   OF   LOW-GRADE   ORES. 

ing  determined  by  the  cost  of  the  pyrite  and  salt  necessary.  The 
consideration  of  lime  content  suggests  another  possible  solution, 
namely,  the  mixing  of  different  ores  in  suitable  combinations. 

Magnesium  compounds  are  similar  in  their  action  to  calcium  com- 
pounds and  the  remarks  on  lime  apply  to  magnesium  equally  well. 

Arsenic  and  antimony  do  not  seem  to  be  of  much  importance  in  a 
consideration  of  this  process  as  applied  to  Utah  ores.  However,  it 
may  be  stated  that  arsenic  and  antimony  compounds  when  present  in 
small  amounts  usually  volatilize  as  chlorides. 

Zinc  sulphide  is  not  affected  by  chloridizing  shaft  roasting,  whereas 
zinc  oxide  is  converted  to  a  chloride  that  is  very  volatile.  Leaching 
with  an  acidified  brine  after  roasting  recovers  less  zinc  than  may  be 
obtained  by  leaching  the  raw  ore. 

Lead  sulphide  becomes  mostly  converted  to  sulphate  in  the  roast- 
ing, owing  to  the  oxidizing  effect  of  the  air  blast.  The  sulphate  does 
not  react  with  the  sodium  chloride  in  roasting.  Lead  oxide  may  be 
formed,  capable  of  being  chloridized ;  but  both  oxide  and  chloride  are 
volatile.  Although  at  the  Park  City  plant  about  40  per  cent  of  the 
low  lead  content  (0.72  per  cent  in  original  ore)  goes  into  solution,  the 
extraction  from  solution  by  means  of  the  iron-box  precipitation  is 
stated  to  be  inefficient.  Electrolytic  methods  of  precipitating  lead 
are  under  consideration  at  that  plant. 

Pyrite  in  the  ore  is  advantageous  in  providing  sulphur  for  the  reac- 
tions, for  neutralizing  lime  and  magnesium,  and  for  combustion,  thus 
lowering  the  amount  of  fuel  necessary.  Sulphur  in  excess  of  that 
necessary  for  the  foregoing  purposes  lengthens  the  period  of  roast- 
ing but  the  sulphur  in  the  escaping  fumes  may  be  utilized  in  the 
generation  of  sulphuric  acid  for  the  leaching. 

Slimy  ores  that  prohibit  percolation  would  require  a  variation  of 
the  Holt  process — some  method  of  agitation  and  vacuum  filtration. 

Water  is  required  in  the  reaction,  and  also  to  ball  up  the  slime  so 
as  to  make  a  product  suitable  for  the  furnace  charge  and  a  calcine 
suitable  for  leaching. 

SUMMARY. 

The  Holt  process  seems  successful  as  regards  extractions  of  copper, 
silver,  and  gold  in  low-grade  ores,  and  in  addition  recovers  a  small 
part  of  the  lead.  The  process  is  especially  adaptable  to  siliceous  ores 
containing  pyrite  enough  to  provide  the  sulphur  necessary  for  the 
sulphatization  that  precedes  the  chloridization. 

Limestone  and  magnesium  are  detrimental,  but  ores  containing 
these  substances  may  be  successfully  treated  if  sulphur  can  be  eco- 
nomically added. 

With  the  proper  conditions  as  indicated,  a  recovery  of  90  to  92 
per  cent  of  the  total  copper,  silver,  and  gold  content,  seems  usually 


METALLURGICAL  TREATMENT  OF   THE   ORES.  31 

possible.  As  regards  copper,  silver,  and  gold,  the  limit  of  applica- 
tion of  the  process  within  the  allowable  limits  as  stated  herein  will 
usually  be  the  cost  of  treatment.  Where  salt  and  coal  are  available 
at  low  costs,  especially  if  ores  of  differing  compositions  are  available 
for  mixing  so  that  the  important  reactions  can  be  naturally  regulated, 
the  chloridizing  process  should  be  hard  to  equal  in  efficiency. 

KNIGHT-CHRISTENSEN  PROCESS. 

The  mines  of  Godiva  Hill  produce  much  siliceous  ore  carrying 
silver.  Although  a  market  for  such  ore  has  been  developed  through 
the  operation  of  the  basic-lined  converter,  the  amount  smelted  is 
comparatively  small.  The  quantity  of  this  ore  has  encouraged  much 
research  on  improved  methods  of  treatment.  A  series  of  analyses  of 
these  ores,  accompanied  by  tests  of  methods  of  treatment,  was  made 
by  N.  C.  Christensen  in  the  metallurgical  laboratories  of  the  Univer- 
sity of  Utah.  As  a  result  of  these  tests  a  new  mill  has  been  erected 
just  above  Silver  City  for  the  treatment  by  the  Knight- Christensen 
process  of  100  tons  of  these  siliceous  ores  daily.  At  this  mill  the  ore 
is  crushed  to  20  mesh,  mixed  with  salt  and  pyrites,  and  the  mixture 
roasted  in  a  new  type  of  furnace  designed  for  the  chloridizing  roast- 
ing of  this  ore.  The  furnace  consists  of  an  annular  screen  hearth  4 
feet  wide,  20  feet  in  outer  diameter,  and  12  feet  in  inner  diameter. 
On  the  hearth  a  thin  layer  of  limestone  is  spread  and  the  layer  of  ore 
is  built  up  to  a  depth  of  4  inches.  A  crude-oil  burner,  which  extends 
across  the  hearth  next  to  the  feed  hopper,  gives  a  flame  hot  enough 
to  start  the  roasting  of  the  admixed  sulphides.  The  reactions  be- 
tween the  salt  and  the  roasting  sulphides  give  a  chloridizing  atmos- 
phere for  the  complete  chloridization  of  the  silver  and  copper  in  the 
ore.  Air  is  drawn  through  the  roasting  mixture  by  a  suction  fan 
and  the  fumes  are  carried  to  the  acid  towers,  where  they  are  ab- 
sorbed and  collected  in  tower  liquors.  The  acidified  liquors  are  car- 
ried to  the  storage  tanks,  where  they  are  brought  up  to  the  required 
strength,  then  being  ready  for  the  leaching  tanks.  The  roasted  ore  is 
transferred  to  the  leaching  tanks  and  the  silver  and  copper  are 
leached  out  with  the  acidified  salt  solution.  The  metals  are  thrown 
down  by  means  of  scrap  iron  in  a  series  of  tanks  that  extend  length- 
wise of  the  building.  The  spent  liquors  are  used  again  for  leaching 
a  new  batch  of  ore,  after  being  brought  up  to  proper  strength  in  the 
towers,  by  the  addition  of  the  necessary  salt. 

The  novel  feature  of  the  mill  is  the  method  of  chloridizing  the  ore 
and  the  use  of  salt  acid  tower  liquors  for  leaching. 

The  successful  operation  of  this  mill  is  anxiously  awaited  by  the 
many  mine  owners  near  by  who  have  an  abundance  of  ore  of  similar 
character. 


32  TREATMENT  OF   LOW-GRADE    ORES. 

PROCESSES   HAVING   A    POSSIBLE   APPLICATION    TO    UTAH    ORES. 

One  of  the  first  things  done  by  the  department  of  metallurgical 
research  of  the  University  of  Utah,  was  to  make  a  search,  as 
thorough  as  the  facilities  of  the  university  library  would  permit,  for 
information  on  processes  that  might  possibly  be  applied  to  the  treat- 
ment of  the  low-grade  and  complex  ores  of  Utah.  The  literature 
relating  to  patents  on  the  subject  was  also  studied.  In  the  following 
statement  an  attempt  is  made  to  outline  concisely  the  possible  appli- 
cation to  Utah  ores  of  processes  which  are  now  in  use,  or  have  been 
suggested. 

LEAD   CARBONATES   CARRYING   SILVER. 

Analysis  of  the  ores  treated  at  the  old  Ontario  mill  in  Park  City 
shows  much  lead  and  silver.  Only  a  very  small  proportion  of  the 
lead  is  being  recovered  and  its  recovery  constitutes  one  of  the 
problems  that  now  face  the  management.  It  is  somewhat  doubtful 
if  a  chloridizing  and  leaching  process  can  recover  the  lead  in  these 
ores,  as  has  been  mentioned  elsewhere  in  this  report. 

MUREX  PROCESS. 

A  process  of  considerable  interest  known  as  the  Murex  process 
has  been  described  lately  which,  it  is  claimed,  will  recover  lead  car- 
bonates. This  process  combines  oil  selection  and  magnetic  separation. 

SULPHIDIZING  AND  FLOTATION. 

Preliminary  tests  have  indicated  the  possibility  of  recovering  lead 
carbonate  by  "  sulphidizing  and  flotation."  The  method  involves  a 
conversion  of  the  oxidized  lead  minerals  into  sulphides  by  means 
of  hydrogen  sulphide  gas,  which  is  cheap,  followed  by  ordinary 
flotation  of  these  artificial  sulphides.  Further  work  is  to  be  done 
along  this  line  and  the  indications  are  that  the  method  may  be  a 
success. 

ELECTROSTATIC  SEPARATION. 

Electrostatic  separation  of  the  lead  carbonates  carrying  silver  is 
another  method  which  has  not  been  tested  completely.  As  it  is 
possible  to  modify  the  outside  coating  on  particles  of  lead  carbonate 
by  the  sulphidizing  process  mentioned  above,  they  ought  to  act  as 
conductors  and  hence  allow  electrostatic  separation  from  the  gangue 
minerals  in  case  it  is  not  possible  to  separate  them  by  flotation,  as 
above  mentioned. 


METALLURGICAL  TREATMENT  OF   THE   ORES.  33 

OXIDIZED    COPPER   ORES    CARRYING    GOLD   AND   SILVER. 
CHLORIDIZING   AND   LEACHING. 

As  may  be  seen  by  reference  to  other  parts  of  this  report,  the 
chloridizing  and  leaching  process  is  especially  applicable  to  oxidized 
copper  ores  carrying  gold  and  silver,  and  high  extractions  of  all  three 
metals  can  be  obtained,  provided  the  ore  is  not  too  basic. 

SULPHIDIZING  AND  FLOTATION. 

Sulphidizing  and  flotation  of  these  oxidized  copper  minerals  also 
seems  to  be  possible.  Preliminary  tests  have  resulted  favorably,  and 
further  tests  are  proposed.  The  presence  of  a  basic  gangue  would 
not  affect  this  process  in  the  least,  as  hydrogen  sulphide  does  not 
attack  limestone.  The  process  would  hence  be  desirable  because  of 
its  applicability  to  ores  of  almost  every  kind  of  gangue. 

MOSHER-LUDLOW  PROCESS. 

The  Mosher-Ludlow  process  was  worked  out  for  those  ores  under 
consideration  which  have  a  basic  gangue,  and  involves  leaching 
with  ammoniacal  solution  carrying  cyanide.  The  ammonia  dis- 
solves copper  and  the  cyanide  dissolves  gold  and  silver.  Precipita- 
tion of  the  copper  is  effected  by  boiling,  the  ammonia  being  recovered. 
Tests  indicate  a  high  extraction  of  all  three  metals  and  a  low  con- 
sumption of  ammonia  and  cyanide.  This  process  has  not  yet  been 
used  on  a  commercial  scale  and  there  is  some  question  as  to  the 
difficulties  of  handling  it  in  a  large  mill. 

SLATER  PROCESS. 

Another  process  that  may  apply  equally  well  to  basic  and  acid  ores 
is  the  Slater  process,  as  the  leaching  agent  is  hypochlorous  acid,  which 
dissolves  copper  and  gold  but  does  not  attack  calcite.  The  process 
is  being  developed  by  the  Western  Precipitation  Co.,  which  is  to  test 
representative  samples  of  Utah  ores.  Tests  indicate  a  good  extrac- 
tion of  the  metals  but  difficulties  still  remain  as  regards  the  type  of 
cells  to  be  used  in  generating  the  hypochlorous  acid. 

OTHER  PROCESSES. 

Other  special  processes  are  possible,  such  as  the  leaching  of  the 
copper  with  dilute  sulphuric  acid  and  the  cyaniding  of  the  tailings. 
As  a  rule  those  ores  of  copper,  silver,  and  gold  that  present  a  prob- 
lem to  the  metallurgist  are  the  ones  that  are  too  low  grade  to  smelt, 
and,  as  a  rule,  the  problem  in  cyaniding  them  is  high  recovery  with- 


34  TREATMENT   OF   LOW-GRADE   ORES. 

out  a  great  consumption  of  cyanide  through  the  action  of  copper 
minerals.  Preliminary  leaching  of  the  copper  is  hence  one  logical 
solution,  and  will  be  tried  out  in  a  mill  at  Dayton,  Nev.,  in  the  near 
future. 

OXIDIZED  ZINC  ORES,  OCCASIONALLY  CARRYING  GOLD  AND  SILVER. 
IGNEOUS  CONCENTRATION. 

Igneous  concentration  seems  at  present  one  of  the  most  feasible 
methods  of  concentrating  earthy  oxidized  zinc  ores,  occasionally  car- 
rying gold  and  silver.  It  involves  the  use  of  blast  grates,  such  as  are 
used  in  the  manufacture  of  zinc-oxide  pigment.  Very  few  experi- 
ments have  been  made  with  this  method,  but  it  is  believed  that  the 
cost  of  treatment  can  be  reduced  to  a  small  figure,  enabling  the  treat- 
ment of  low-grade  ores  of  zinc.  Any  gold  or  silver  remains,  of 
course,  in  the  residue  left  after  removal  of  the  zinc,  and  can  then  be 
recovered  by  smelting.  In  case  the  gold  and  silver  contents  were  too 
small  to  make  smelting  the  residue  profitable,  special  processes  would 
have  to  be  devised  to  recover  them. 

LEACHING  WITH  AMMONIUM   CARBONATE   SOLUTION. 

Leaching  out  the  zinc  with  a  solution  of  ammonium  carbonate  and 
ammonia  is  easily  accomplished  when  the  oxidized  zinc  mineral  con- 
sists of  smithsonite,  the  carbonate  of  zinc,  but  the  silicates  of  zinc  are 
not  attacked.  Gold  and  silver  can  then  be  leached  from  the  residue 
or  it  can  be  smelted.  Some  rather  extensive  tests  of  this  process  have 
been  made  at  Ingot,  Cal.a 

BISULPHITE  PROCESS. 

At  Swansea,  Wales,  a  process  has  recently  been  brought  to  more  or 
less  technical  success  whereby  zinc  is  dissolved  in  a  solution  of  sul- 
phur-dioxide gas  obtained  by  passing  the  gases  from  the  roasting  of 
sulphide  ores  through  a  falling  spray  of  water  in  a  tower.  The 
zinc  dissolves  in  this  solution  and  is  easily  recovered.  Where  the 
oxidized  ores  can  be  treated  in  conjunction  with  sulphide  ores,  this 
process  promises  to  have  some  value,  if  sufficiently  low  costs  are  indi- 
cated by  present  experiments  in  Wales.  No  tests  of  Utah  ores  have 
as  yet  been  made. 

LEACHING  WITH  ACID  SOLUTION  Atfb  ELECTROLYTIC  PRECIPITATION  OF  ZINC. 

A  great  many  processes  are  being  tried  out  in  which  either  sul- 
phuric or  hydrochloric  acid  is  used  as  a  solvent  for  zinc,  the  zinc 

0  Bretherton,  S.  E.,  Tin-  t  K  utim nt  of  complex  ores  by  the  ammonia-carbon  dioxide 
process  :  Bull.  Am.  Inst.  Min.  Eng.,  July,  1914,  p.  1771. 


METALLURGICAL  TREATMENT  OF   THE   ORES.  35 

being  later  precipitated  from  solution  by  an  electric  current.  Success 
will  depend  on  very  careful  engineering,  as  the  amount  of  electric 
energy  necessary  to  precipitate  zinc  is  large  in  comparison  with  the 
value  of  the  resulting  metal.  Large  scale  production  and  cheap  elec- 
tric energy  and  acid  will  have  to  be  obtained  to  insure  financial  suc- 
cess. Technically  these  processes  work  very  well. 

OXIDIZED    ZINC-LEAD    ORES,    CARRYING    OCCASIONALLY    GOLD    AND    SILVER. 


The  main  problem  in  treating  oxidized  zinc-lead  ores,  carrying 
occasionally  gold  and  silver,  is  to  obtain  the  zinc  and  the  lead  as 
separate  products.  On  that  account  processes  in  which  only  one  of 
these  metals  is  dissolved  are  preferable. 

BISULPHITE   PROCESS. 

The  bisulphite  process  previously  mentioned  dissolves  only  the 
zinc  and  was,  in  fact,  devised  for  the  treatment  of  complex  zinc-lead 
sulphides.  The  zinc  is  dissolved  out  and  precipitated.  The  residue 
left  contains  all  the  lead,  silver,  and  gold  of  the  ore  and  can  be  smelted 
in  an  ordinary  lead  blast  furnace.  The  metallurgical  research  depart- 
ment plans  to  try  this  process  on  the  Utah  ores  later. 

LEACHING    WITH    AMMONIUM    CARBONATE    SOLUTION. 

In  leaching  with  ammonium  carbonate  solution  the  zinc  is  sepa- 
rated from  the  other  metals  as  in  the  bisulphite  process.  As  zinc 
interferes  with  the  metallurgy  of  almost  all  of  the  other  metals,  this 
process  would  seem  to  be  a  desirable  one  for  such  ores. 

SULPHIDIZING    AND    FLOTATION. 

Sulphidizing  and  flotation,  as  previously  mentioned,  has  been 
found  to  remove  lead  minerals  but  not  to  affect  zinc  minerals,  and 
hence  offers  another  method  of  separating  lead  and  zinc.  As  the 
silver  and  gold  are  quite  likely  to  accompany  the  lead,  the  process 
would  seem  to  offer  a  most  desirable  type  of  mechanical  concentra- 
tion, provided  the  lead  and  zinc  minerals  can  be  separated  from  each 
other  by  sufficiently  fine  grinding. 

OXIDIZED  ORES  OF  ZINC  AND  COPPER,  CARRYING  GOLD  AND  SILVER. 
LEACHING    WITH    AMMONIUM    CARBONATE    SOLUTION. 

In  the  ammonium  carbonate  process  described  both  the  zinc  and 
copper  are  dissolved,  but  they  are  easily  separated  by  electrolysis  as 
the  metallic 'copper  will  deposit  on  the  zinc.  The  gold  and  silver 
will  remain  in  the  residue,  and  can  be  recovered  by  leaching  or 
smelting.  Tests  of  this  process  on  the  Utah  ores  have  not  been  made 
as  yet  by  the  metallurgical  research  department  of  the  University 
of  Utah. 


36  TREATMENT  OF   LOW-GRADE   ORES. 

BISULPHITE  PROCESS. 

The  bisulphite  process  will  also  dissolve  both  the  copper  and  the 
zinc,  and  as  they  are  easily  separated,  the  remarks  on  the  ammo- 
nium carbonate  process  apply  here  as  well. 

LEACHING    WITH    ACID    SOLUTION   AND   ELECTROLYTIC   PRECIPITATION. 

Leaching  out  the  zinc  and  copper  with  acid  solution,  followed 
by  electric  precipitation  of  the  zinc  and  copper,  separately,  seems 
feasible.  Copper  can  be  precipitated  completely  in  the  presence  of 
zinc  without  any  zinc  being  precipitated,  because  the  voltage  required 
to  decompose  the  zinc  salts  is  much  higher  than  that  required  for 
the  copper  salts. 

IGNEOUS    CONCENTRATION. 

Igneous  concentration  of  the  zinc  content  is  supposed  to  be  per- 
fectly feasible  with  these  ores,  the  copper,  gold,  and  silver  being  left 
in  the  residue.  As  this  residue  is  likely  to  be  partly  fused,  nothing 
but  smelting  can  recover  the  copper,  gold,  and  silver.  Hence  the 
ore  must  be  of  high  enough  grade  to  stand  the  smelting  costs ;  other- 
wise, one  of  the  leaching  processes  should  be  better. 

OXIDIZED   ORES   CARRYING   ZINC,   COPPER,   LEAD,    SILVER,   AND   GOLD. 

In  these  ores,  the  presence  of  zinc  is  again  the  disturbing  factor, 
and  its  removal  separate  from  the  other  metals  eliminates  most  of 
the  difficulty.  As  mentioned  above,  both  the  bisulphite  process  and 
the  ammonium  carbonate  process  under  certain  conditions  remove 
zinc  and  copper,  and  these  two  metals  are  easily  separated  from 
each  other.  It  would  therefore  seem  feasible  to  apply  these  two 
processes  to  this  class  of  ores.  Sulphidizing  and  flotation  would 
seem  to  be  a  very  promising  method  of  removing  the  lead,  copper, 
gold,  and  silver  from  the  zincky  residue. 

PARTLY  OXIDIZED  SULPHIDE  ORES. 

Very  few  of  the  processes  mentioned  work  well  on  both  sulphide 
and  oxidized  ores  except  igneous  concentration,  which  should  remove 
zinc  as  a  clean  product  from  any  ore  that  is  not  too  high  in  lead. 
All  of  the  other  processes  discussed  would  doubtless  require  the 
ore  to  be  roasted  before  they  could  be  applied.  Also,  most  of  the 
sulphide  minerals  could  be  removed  by  ordinary  methods  of  gravity 
concentration  before  processes  for  the  oxidized  minerals  were 
applied. 

RAW  MATERIALS  FOR  USE  AS  REAGENTS. 

The  State  of  Utah  has  within  its  borders  abundant  supplies  of 
minerals  that  may  be  employed  as  reagents  in  processes  for  extract- 


METALLURGICAL   TREATMENT  OF    THE   ORES.  37 

ing  metals  from  ores.  The  tremendous  salt  supply  in  the  waters  of 
the  Great  Salt  Lake  and  in  the  deposits  near  by  was  for  many  years 
put  to  good  use  in  the  ore-reducing  mills.  New  processes  employ- 
ing increased  amounts  of  salt  are  coming  into  use.  The  salt  and 
associated  mirabilite  (NaSO4)  will  serve  as  the  raw  material  from 
which  chemical  works  can  make  sodium  carbonate,  hydrochloric  acid, 
hypochlorous  acid,  iron  chloride,  and  such  chlorides,  perchlorates, 
chlorates,  etc.,  as  may  be  needed  in  leaching  ores.  A  process  for  the 
manufacture  of  hydrochloric  acid  from  common  salt,  silica,  and  steam 
has  been  evolved  in  the  research  laboratories  of  the  university  which 
bids  fair  to  provide  for  making  this  acid  at  a  cost  well  below  the 
present  cost  of  manufacture.  The  sulphur  gases  from  smelter 
smoke  carry  the  constituents  for  the  manufacture  of  sulphuric  acid, 
the  acid  most  used  in  leaching  plants.  In  localities  near  plants 
smelting  sulphide  ore  the  price  of  sulphuric  acid  may  possibly  be 
brought  to  a  nominal  figure.  The  removal  of  sulphur  gases  from 
smelter  fumes  to  make  sulphuric  acid  will  largely  reduce  the  harmful 
effects  of  smelter  smoke  on  vegetation. 

IRON  FOR  PRECIPITATION. 

By  a  process  of  chemical  replacement  the  gold,  silver,  and  copper 
of  the  leaching  solutions  may  be  deposited  by  metallic  iron.  Scrap 
iron  has  been  used  extensively  in  regions  where  it  is  cheap.  In  the 
mining  districts  of  Utah  the  amount  of  scrap  iron  to  be  obtained 
would  be  very  small. 

Within  the  State,  accessible  from  Salt  Lake  City  and  vicinity,  are 
large  amounts  of  ores  suitable  for  the  production  of  sponge  iron,  as 
both  sulphide  and  oxidized  iron  ore  and  copper-bearing  sulphides 
are  suitable  for  this  purpose.  An  economic  saving  is  made  if  the 
ores  contain  gold,  silver,  or  copper,  these  metals  being  all  saved,  and 
without  added  cost,  if  the  iron,  preferably  sponge  iron,  made  from 
the  ores  is  used  as  a  precipitant  in  leaching  processes. 

In  the  July,  1914,  number  of  the  Bulletin  of  the  American  Institute 
of  Mining  Engineers  Frederick  Laist  and  F.  F.  Frick  present  the 
following  description0  of  a  method  they  worked  out  for  the  manu- 
facture of  sponge  iron: 

The  furnace,  a  Bruckner  type,  4  feet  3  inches  in  diameter  inside  and  1  feet 
long,  is  operated  as  follows: 

One  thousand  four  hundred  pounds  of  calcine  are  charged  and  heated  with 
fuel-oil  flame  to  about  1,300°  F.  This  requires  about  one  and  one-fourth  hours. 
In  a  commercial  plant  the  calcine  would  be  drawn  hot  directly  from  the 
MacDougall  hoppers  to  the  furnace.  About  600  pounds  of  coal  are  then  shov- 
eled in  through  the  front  in  small  lots.  The  furnace  continues  to  revolve,  and 
in  about  three-quarters  of  an  hour  after  starting  to  charge  the  coal  the  hydro- 

0  Precipitation  of  copper  from  solution  at  Anaconda,  p.  1433. 


38  TREATMENT  OF    LOW-GRADE   ORES. 

carbons  are  burned  off.  The  oil  flame  is  again  started.  In  one  and  three- 
fourths  to  two  hours  the  charge  is  up  to  1,680°  to  1,700°  F.,  and  reduction  is 
complete.  The  discharging  door  is  removed  and  the  charge  quenched. 

SODIUM   SULPHATE    (MIRABILITE) . 

Next  to  common  salt,  sodium  sulphate  suggests  itself  -as  a  profit- 
able product  of  the  water  of  Great  Salt  Lake.0  This  substance 
(known  mineralogically  as  mirabilite)  separates  from  the  brine  at  a 
certain  low  temperature.  This  critical  temperature  is  probably 
within  a  few  degrees  of  the  freezing  point  of  fresh  water. 

As  the  crystallization  of  the  mirabilite  proceeds  the  water  becomes 
opalescent,  and  the  substance  deposits  over  the  lake  bed  and  is  cast 
up  by  the  waves  in  such  quantities  as  to  cover  the  shore  in  places  to  a 
depth  of  inches  or  even  feet.  It  can  be  easily  gathered  by  the  use 
of  horse  drags. 

The  easy  preparation  of  sodium  carbonate  from  mirabilite  is  self- 
suggestive,  and  experience  has  demonstrated  the  success  of  the 
undertaking  at  low  cost.  Limestone  and  coal  necessary  to  trans- 
form the  sulphate  into  carbonate  are  of  easy  access. 

ALLIED   PROBLEMS. 

In  taking  up  an  industrial  problem  one  generally  finds  that 
there  are  many  allied  problems  awaiting  solution,  and  this  has 
proved  to  be  especially  true  of  the  investigation  to  ascertain  the 
feasibility  of  attempting  to  treat  the  low-grade  and  complex  ores  of 
the  State  of  Utah.  To  illustrate — certain  electrometallurgical  proc- 
esses demand  cheap  power.  Such  being  the  case,  information  is 
needed  as  to  the  availability  of  electric  power  either  from  the  utili- 
zation of  flowing  streams  or  from  the  coal  resources  of  the  State. 
Again,  with  the  question  of  hydroelectric  power  may  be  connected 
the  question  of  irrigation,  as  at  The  Dalles,  Greg.,  and  the  working 
up  of  this  possibility  alone  may  require  considerable  investigation. 
If  coal  is  to  be  utilized,  the  location  of  available  coal  beds,  the  nature 
of  the  coal,  and  the  possible  utilization  of  the  by-products  from  the 
distillation  of  the  coal  become  of  interest. 

Incidentally,  the  problem  of  utilizing  such  by-products  of  coal 
as  ammonia,  tars,  and  tar  oils  is  closely  connected  with  metallurgical 
processes,  as  ammonia  can  be  used  very  well  in  the  extraction  of 
metals  from  oxidized  ores,  both  of  copper  and  of  zinc,  and  certain 
coal-tar  products  are  in  demand  for  flotation  work.  A  proper  inves- 
tigation might  show  that  it  would  prove  profitable  to  save  these  mate- 
rials in  the  coking  of  the  coals  instead  of  letting  all  of  the  volatile 
part  of  the  coal  be  wasted,  as  it  is  at  present  in  the  preparation  of 
coke  in  Utah,  Nevada,  Idaho,  and  Montana. 

"Talmage,  .T.  E.,  The  Great  Salt  Lake,  1000,  pp.  64-S5,  82-86. 


METALLURGICAL   TREATMENT  OF   THE   ORES.  39 

In  the  coking  of  coal  it  may  be  possible  to  find  a  solution  of  the 
smoke  problem  in  the  city  of  Salt  Lake,  as  coke  and  gas  fuels  are 
smokeless,  whereas  the  raw  soft  coals  of  the  State,  which  are  now 
being  used,  make  the  city  atmosphere  very  smoky  under  certain 
conditions  in  wintertime.  The  department  of  metallurgical  re- 
search, in  cooperation  with  the  Federal  Bureau  of  Mines,  is  at  pres- 
ent engaged  in  an  investigation  of  this  nature. 

Again,  as  regards  the  use  of  electric  energy  in  the  preparation  of 
solvents  from  the  waters  of  Great  Salt  Lake  for  the  purpose  of  treat- 
ing ores,  there  are  likely  to  be  by-products  formed  which  can  be 
used  in  other  industries  in  the  State.  As  an  instance,  sodium  hy- 
drate, chlorine,  or  hydrochloric  acid  can  be  used  in  making  phosphate 
rock  soluble  and  available  for  use  as  fertilizer,  although  this  can  also 
be  done  with  sulphuric  acid,  which  can  be  cheaply  made  by  treat- 
ment of  the  smoke  from  furnaces  for  sulphide  ores. 

As  is  well  known,  in  the  eastern  part  of  the  State  are  extensive 
deposits  of  hydrocarbons.  In  hydrometallurgical  work  it  is  gener- 
ally necessary  to  use  large  vats.  Concrete  has  proven  satisfactory 
for  the  construction  of  such  vats,  but  if  acid  solutions  be  used,  the 
vats  must,  of  course,  have  an  acid-proof  lining.  It  is  stated  that 
the  use  of  asphalt  for  this  purpose  has  given  excellent  results. 
Hence  the  hydrocarbons  of  Utah  may  become  an  important  source 
of  acid-resistant  lining. 

A  large  number  of  such  instances  might  be  cited  to  show  how  in- 
vestigations conducted  for  the  purpose  of  solving  the  low-grade  ore 
problem  may  result  in  the  discovery  of  unsuspected  uses  for  other 
natural  resources  of  the  State. 

CONCLUSION. 

As  shown  by  its  title,  this  paper  is  offered  only  as  a  preliminary 
report.  Its  purpose  is  to  give  some  idea  of  the  size  and  extent  of  the 
low-grade  ore  deposits  of  the  State,  and  the  necessity  of  conducting 
investigations  for  the  purpose  of  discovering  processes  that  will  be 
commercially  suited  to  the  treatment  of  these  ores  and  of  developing 
such  other  industries  as  may  be  brought  about  as  the  result  of  carry- 
ing on  the  investigations. 


PUBLICATIONS    ON    TREATMENT    OF    MINERALS. 

A  limited  supply  of  the  following  publications  of  the  Bureau  of 
Mines  is  temporarily  available  for  free  distribution.  Bequests  for 
all  publications  can  not  be  granted,  and  to  insure  equitable  distribu- 
tion applicants  are  requested  to  limit  their  selection  to  publications 
that  may  be  of  especial  interest  to  them.  Requests  for  publications 
should  be  addressed  to  the  Director,  Bureau  of  Mines. 

BULLETIN  3.  The  coke  industry  of  the  United  States  as  related  to  the  foundry, 
by  Richard  Moldenke.  1910.  32  pp. 

BULLETIN  12.  Apparatus  and  methods  for  the  sampling  and  analysis  of  fur- 
nace gases,  by  J.  C.  W.  Frazer  and  E.  J.  Hoffman.  1911.  22  pp.,  6  figs. 

BULLETIN  47.  Notes  on  mineral  wastes,  by  C.  L.  Parsons.     1912.    44  pp. 

BULLETIN  53.  Mining  and  treatment  of  feldspar  and  kaolin  in  the  southern 
Appalachian  region,  by  A.  S.  Watts.  1913.  170  pp.,  16  pis.,  12  figs. 

BULLETIN  64.  The  titaniferous  iron  ores  of  the  United  States,  their  composi- 
tion and  economic  value,  by  J.  T.  Singewald,  jr.  1913.  145  pp.,  16  pis.,  3  figs. 

BULLETIN  70.  A  preliminary  report  on  uranium,  radium,  and  vanadium,  by 
R.  B.  Moore  and  K.  L.  Kithil.  1913.  101  pp.,  4  pis.,  2  figs. 

BULLETIN  71.  Fuller's  earth,  by  C.  L.  Parsons.     1913.     38  pp. 

BULLETIN  77.  The  electric  furnace  in  metallurgical  work,  by  D.  A.  Lyon, 
R.  M.  Keeney,  and  J.  F.  Cullen.  1914.  217  pp.,  56  figs. 

BULLETIN  81.  The  smelting  of  copper  ores  in  the  electric  furnace,  by  D.  A. 
Lyon  and  R.  M.  Keeney.  1914.  80  pp.,  6  figs. 

BULLETIN  84.  Metallurgical  smoke,  by  C.  H.  Fulton.  1914.  90  pp.,  5  pis., 
15  figs. 

TECHNICAL  PAPER  41.  Mining  and  treatment  of  lead  and  zinc  ores  in  the  Joplin 
district,  Missouri,  a  preliminary  report,  by  C.  A.  Wright.  1913.  43  pp.,  5  figs. 

TECHNICAL  PAPER  50.  Metallurgical  coke,  by  A.  W.  Belden.  1913.  48  pp., 
1  pi.,  23  figs. 

TECHNICAL  PAPER  60.  The  approximate  melting  points  of  some  commercial 
copper  alloys,  by  H.  W.  Gillett  and  A.  B.  Norton.  1913.  10  pp.,  1  fig. 

TECHNICAL  PAPER  81.  The  vapor  pressure  of  arsenic  trioxide,  by  H.  V.  Welch 
and  S.  H.  Duschak.  1915.  22  pp.,  2  figs. 

TECHNICAL  PAPER  88.  The  radium-uranium  ratio  in  carnotites,  by  S.  C.  Lind 
and  C.  F.  Whittemore.  1915. 

TECHNICAL  PAPER  95.  Mining  and  milling  of  lead  and  zinc  ores  in  the  Wis- 
consin district,  by  C.  A.  Wright.  1915.  39  pp.,  1  pi.,  5  figs. 

40 


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